It looks like there is a great list for acts 1-4 here: Where do the enemies for the unique enemy achievements spawn?
However, I couldn't find a list for the new Act 5 achievements added in Reaper of Souls.
Diablo – Where do the Act 5 Unique monsters spawn for the Special Assignment / Irreplaceable You achievements
achievementsdiablo-3
Related Solutions
According to this forum post and my own experience, they are located as follows:
Judge of Character
- Fuad's Journal - In the random location Fuad's Cellar in Howling Plateau, kill the Unique enemy Fuad and he drops this.
- Zoltun Kulle - In the Hidden Camp, once you begin Betrayer of the Horadrim, it will be on the ground beside Adria.
- The Musings of Sardar - In the random location Tomb of Sardar in the Dahlgur Oasis.
- The Promises of Fezuul al-Kazaar - Kill the unique Grotesque Fezuul that spawns at a randomly occurring puddle of water with a number of bones in the Dahlgur Oasis. It spawns after you kill the skeletons that will spawn upon investigating the bones.
- Eirena's Journal - Eirena, after the conversation Eirena's Journey available throughout Act II so long as Eirena has been out of the party at least once.
- Iron Wolf Captain's Journal - On the northern part of Alcarnus, you will find the Iron Wolf's Captain's Corpse which will drop this journal.
- The Legend of Zei the Trickster - Shen, after his conversation A Case of Mistaken Identity which is available from the start of Act II.
- Kala's Poem - Kala (North side of Hidden Camp), after her conversation Noble Dreams from the end of Betrayer of the Horadrim and during the quest Blood and Sand.
- The Last Will of Khan Dakab - In the random location Tomb of Khan Dakab in the Dahlgur Oasis.
- Larra's Diary - In a random Deserted Cellar with the merchant Larra in Black Canyon Mines after you talk to the merchant Larra who appears there. (seems to be always the northern cellar)
- Kulle's Journal Part 1 - At the End of Vault of the Assassin.
- Kulle's Journal Part 2 - At the start of Cave of the Betrayer Level 1.
- Kulle's Journal Part 3 - At the end of Cave of the Betrayer Level 2.
- Kulle's Journal Part 4 - Drops from the defeated Zoltun Kulle in Archives of Zoltun Kulle.
- Leah's Journal (8-12) - Right side of the Hidden Camp during major missions. Certain ones are available during certain quests..
- Part 8. During Shadows in the Desert.
- Part 9. During The Road to Alcarnus (from Find the Khasim Outpost) & City of Blood.
- Part 10. During Unexpected Allies & Betrayer of the Horadrim.
- Part 11. During Blood and Sand & The Black Soulstone.
- Part 12. During The Scouring of Caldeum until the end of Act II.
- The Seven Lords of Hell, Belial the Lord of Lies, Azmodan the Lord of Sin, Diablo the Lord of Terror, Andarial the Maiden of Angish, Duriel the Lord of Pain, Mephisto the Lord of Hatred, and Baal the Lord of Destruction - Cain's Lost Satchels throughout the act. The books are sequenced and it doesn't matter where you pick them up.
- I just did a playthrough of Act II and I've seen them in:
- near the ceremonial circle in Secret Altar (Howling Plateau),
- south of the Khasim Outpost waypoint,
- the random dungeon The Ruins Levels 1 and 2 (Stinging Winds),
- The Crumbling Vault (and Vault Treasure Room)(Stinging Winds),
- south of the Road to Alcarnus waypoint,
- north west of the merchant in Flooded Causeway,
- Ruined Cistern,
- east of Path to the Oasis waypoint,
- The Forgotten Ruins,
- Vault of The Assassin.
- I also recall finding them in some of the non-cave (in appearance) dungeons during previous playthroughs such as:
- Chamber of the Lost Idol(Stinging Winds),
- Tomb of Sardar(Dahlgur Oasis),
- the Tomb of Khan Dakab(Dahlgur Oasis).
- I just did a playthrough of Act II and I've seen them in:
- A Love Letter - Dahlgur Oasis, Keepsake Box
- Necromancer's Log - Stinging Winds in a random event location, after you complete the event The Restless Sands, Mehtan the Necromancer will drop this.
- The Imperial Guard's Orders - From an encounter in Dahlgur Oasis or one of its cellars.
- Crumbling Journal - You collect this from Skeletal Remains in Desolate Sands.
- Poltahr's Notes - In the random location Chamber of the Lost Idol in Stinging Winds.
- The Ancient Portal Device - Beside the Ancient Device that can randomly be found in Desolate Sands.
- Blackened Journal - From a Charred Iron Wolf Corpse on the west side of the Caldeum Bazaar that can be found during The Scouring of Caldeum.
- A Servant's Journal - From a Crumpled Corpse on the north side of the Caldeum Bazaar until the quest Unexpected Allies.
Historian of Caldeum
- The Desert Aqueducts Part 1 and Part 2 - In Western Channel and Eastern Channel of the Hidden Aqueducts. These are sequenced so it doesn't matter which satchel you find first or if you find the same one twice.
- An Abridged History of Caldeum (6) - Searing Sands Inn in the Caldeum Bazaar. These books become available as you complete the main quests. If you miss any, they will all be included with the drop of the next one you collect.
- Part 1: From the start of Act II onwards.
- Part 2: From The Road to Alcarnus objective Find Khasim Outpost onwards.
- Part 3: From A Royal Audience onwards.
- Part 4: From Unexpected Allies onwards.
- Part 5: From Betrayer of the Horadrim onwards.
- Part 6: From The Black Soulstone onwards.
- The Dahlgur Oasis - Dahlgur Oasis, Keepsake Box.
- On the Desolate Sands(3) - Desolate Sands, Traveler's Pouches. These are sequenced so you will always get these in order.
- The Chamber of Faces - Dahlgur Oasis, right outside the random location Tomb of Khan Dakab.
Eavesdropper
- Guard's Orders - Imperial Guard Supplies in Khasim Outpost.
- Proclamation from the Imperial Guard - In the south of the Caldeum Bazaar, just outside of the Hidden Camp entrance during A Royal Audience.
- Missive to Maghda Part 1 - Tortured Cultist Courier at the back of The Secret Conclave in Howling Plateau and/or Sandy Cellar in Alcarnus.
- Missive to Maghda Part 2 - Tortured Coven Minion Alcarnus, just south of Maghda's Lair.
- Deciever's Orders Part 1 - Envoy of Belial found in The Sewers of Caldeum.
- Deciever's Orders Part 2 - Envoy of Belial found in Dahlgur Oasis.
- Deciever's Orders Part 3 - Envoy of Belial found in Desolate Sands.
- The Feared Hero - Stinging Winds, random spawn of a cultist camp after the Khasim Outpost.
- Hunter's Journal Part 1 - At the start of The Forgotten Ruins.
- Hunter's Journal Part 2 - Hidden Aqueducts (Western and/or Eastern Channel)
- Hunter's Journal Part 3 - Beside the entrance to Archives of Zoltun Kulle in Desolate Sands.
- Hunter's Journal Part 4 - Beside the Shadow Lock in The Storm Halls in Archives of Zoltun Kulle.
- Hunter's Journal Part 5 - Beside the Shadow Lock in The Unknown Depths in Archives of Zoltun Kulle.
- Hunter's Journal Part 6 - Drops from the guardian in The Forgotten Ruins that spawns after recovering the head of Zoltun Kulle.
There are 82 of these and they are all found randomly. I've added all the ones that I've confirmed personally to start with plus those listed on the Diablo 3 database that I've verified on other sites. For the sake of completeness and simplicity, I'm posting this as a community wiki post so that people can add what they find:
Act I
- Bellybloat the Scarred, Infected Monstrosity - Cathedral Level 4
- Captain Cage, Commander of the Dead - Cathedral Level 4
- Cudgelarm, Undead Mauler - Cathedral Level 2
- Dreadclaw the Leaper, Rodent of Unusual Size - Fields of Misery
- Drury Brown, Thief of Bones - Defiled Crypt
- Ebenezer Samuel, Deceased Scribe - Old Tristram Road / Mass Grave
- Fecklar's Ghost, Horror of the Shadows - The Festering Woods
- Firestarter, Burn to a Cinder - Cathedral Level 2
- Jezeb the Conjuror, Cultist Beast Caller - Leoric's Manor
- Logrut the Warrior, Fierce Moon Clan Fighter - Highlands Crossing / Southern Highlands
- Lorzak the Powerful, Bearer of Frost - Southern Highlands
- Lucious the Depraved, Thief of Corpses - Cemetery of the Forsaken
- Mange, Vicious Infected Beast - The Weeping Hollow
- Merrium Skullthorn, Plagued Skeletal Fighter - Cathedral Level 2
- Qurash the Reviled, Plaguespinner - Caverns of Araneae
- Ragus Grimlow, Gorged Undead Brother - Cathedral Level 1
- Rathlin the Widowmaker, Plagueweaver - Caves of Aranae
- Red Rock, Heart of Fire - Southern Highlands
- Sarella the Vile, Cruel Servant of the Coven - Leoric's Manor Courtyard
- Venimite, Tiny and Deadly - Caverns of Araneae
- Zhelobb the Venomous, Broodspawn of the Queen - Caverns of Araneae
Act II
- Ashek, Diminutive Fallen Fighter - Black Canyon Mines
- Beyatt, The Elusive One - Stinging Winds, Lost Caravan subarea
- Blarg the Imp, Frenetic Fiery Creature - Desolate Sands
- Bloodfeather, Winged Desert Predator - Desolate Sands
- Gart the Mad, Maniacal Fallen Master - Howling Plateau
- Hazzor the Viper, The Sibilant - Sewers of Caldeum
- Hellscream, The Render - The Unknown Depths
- High Cultist Murdos, Cruel and Powerful Cult Acolyte - Alcarnus
- Mage Lord Caustus, Guardian Lord of Poison - The Storm Halls
- Mage Lord Flaydren, Guardian Lord of Lightning - The Storm Halls
- Mage Lord Ghuyan, Guardian Lord of Fire - The Storm Halls
- Mage Lord Skomara, Guardian Lord of Frost - The Storm Halls
- Otzi the Cursed, Infected Creature of Death - Eastern Channel
- Raiha the Vicious, Swiftness of a Cat - Desolate Sands
- Razormouth, Terror of the Sand - Black Canyon Mines
- Saha the Slasher, Infected Terrifying Claws - Howling Plateau
- Sammash, Coven Thug - Alcarnus
- Shondar the Invoker, Master of the Threshold - Alcarnus
- Stinging Death Swarm, Relentless Cloud of Pain - Eastern Channel / Western Channel
- The Archivist, Dark Lorekeeper - The Unknown Depths
- Thrum, Giant Stone Mauler - Realm of Shadow
- Torsar, Storm of the Desert - Dahlgur Oasis
- Yakara, Savage Serpent Warrior - Eastern Channel
- Yeth, Hound of Pestilence - Road to Alcarnus
Act III
- Axegrave the Executioner, Heads Will Roll - The Keep Depths Level 2
- Axgore the Cleaver, Lord of the Phasebeasts - Core of Arreat
- Bashface the Truncheon, Powerful Demon Warrior - Stonefort
- Belagg Pierceflesh, Bone and Arrow - The Keep Depths Level 3
- Blarg the Foul, Diseased Warrior Brute - Bridge of Korsikk
- Captain Dale, Former Guard Captain - The Keep Depths Level 1
- Charuch the Spear, Deadly Blood Clan Ranger - Tower of the Cursed level 1
- Chiltara, Vile Frost Stalker - Caverns of Frost Level 2
- Demonika the Wicked, From the Heart of Hell - Tower of the Damned Level 1
- Direclaw the Demonflyer, Swift Winged Death - Rakkis Crossing
- Dreadgrasp, Tendrils of Evil - The Battlefields
- Gholash, Savage Fiery Brute - Tower of the Damned Level 1
- Gormungandr, Serpent of Arreat - Arreat Crater Level 1
- Gorog the Bruiser, One-Thousand Pounder - The Core of Arreat
- Growlfang, Bite Much Worse Than Bark - Arreat 1
- Gugyn the Gauntlet, Impassable Barrier - The Keep Depths Level 3
- Haxxor, Wielder of Giant Axes - Tower of the Cursed Level 2
- Hyrug the Malformed, Forgotten Scourge - Tower of the Cursed Level 1
- Lummock the Brute, Enraged Bone Breaker - Rakkis Crossing
- Marchocyas, Winged Horror - Skycrown Battlements
- Mehsak the Abomination, From the Depths of Arreat - The Battlefields
- Riplash, Thief of Souls - Tower of the Damned Level 2
- Severclaw, Fiery Crawler - Arreat Crater Level 1
- Shandra'Har, Vile Plagued Conjuror - Rakkis Crossing
- The Crusher, Just Passin' By - Tower of the Damned Level 2
- Thornback, Spiked Fire Beast - The Keep Depths Level 1
- Vicious Gray Turkey, Delicious Armored Beast - The Keep Depths Level 3
Act IV
- Grimnight the Soulless, Shadow of Death - Silver Spire Level 2
- Haures, Hand of Ruin - Silver Spire Level 2
- Khatun, Sky Terror - Gardens of Hope 1st tier
- Kysindra the Wretched, Lust's Forlorn - Silver Spire Level 1
- Pyres the Damned, Eternity of Fire - Silver Spire Level 1
- Rhau'Kye, The Eye of Flame - Silver Spire Level 2
- Sao'Thall, Embodiment of Hatred - Silver Spire Level 2
- Slarg the Behemoth, Massive Hellbeast - Silver Spire Level 1
- Torchlighter, Breath of Flame - Gardens of Hope 2nd Tier (Possibly 1st Tier)
- Veshan the Fierce, Cloaked by the Unseen - Gardens of Hope 1st Tier
If you edit the lists above, please note the specific area and sub-area where you found them.
Best Answer
Here's the list, with some locations collected from http://www.d3andre.com/en/special-assignment-achievement-4.html. I haven't confirmed these locations myself but am making it community wiki so that will be easy to do. I'll put asterisks after locations that are confirmed in the table below.