[RPG] How many enemies can I hit with a Cloud of Daggers

April 2016's Sage Advice expressly defines how this phrase operates and names Cloud of Daggers as one of several spells to which this definition applies.

In summary, a spell like moonbeam affects a creature when the creature passes into the spell’s area of effect and when the creature starts its turn there. You’re essentially creating a hazard on the battlefield.

Furthermore, it is stated that such spells do not damage targets when initially cast.

So this is how it works:

1. Daffy the Wizard casts Cloud of Daggers atop a mighty gorgon. The gorgon takes no damage. (You could say it is 'undeterred'.)

2. Garrosh, an orc barbarian, pushes a murloc into the Cloud of Daggers. The murloc takes damage (and shares the space with the gorgon).

3. The gorgon takes its turn and starts within the Cloud's effect, thus it takes damage. It wisely moves out of that area.

4. The murloc takes its turn and starts within the Cloud's effect, thus it takes damage. It chooses to remain in that space. On its next turn, it will take damage again. (Must be quite the murloc to still be alive.)

Forced Movement

The saving throw is triggered at the beginning of a creatures turn. So if you have a way to move creatures into the cloud, they will not have a chance to move out of it before a saving throw is triggered (unless another force moves them out before their turn rolls around). Using this technique you can lock down enemies for longer than usual. Some ways to forcefully move enemies are:

• The spell Thunderwave is particularly useful in this role as it can affect multiple creatures at once.
• Bigby's Hand is versatile, but to use with stinking cloud will require another caster due to concentration centration as well a second caster will be necessary
• Pushing Attack Battle Master maneuver
• One Hand Technique feature of Open Hand Monks has a push mode
• Thunderous Smite Paladin spell
• Repelling Blast Warlock invocation
• Spells that allow you to dictate what a creature does such as Command, or Dominate Person/Monster
• Shoving a creature by substituting an attack
• Grappling a creature and moving it around (at half speed)

As Fog Cloud+

As you mentioned the spell's area is considered heavily obscured. This means that the spell can be used tactically in much the same way as you would use Fog Cloud.

• If placed on top of a group of enemies with ranged attacks they will be forced to relocate and you can sometimes place it cleverly enough that the area they move to puts them at a disadvantage. It also has the benefit that the enemies will not be able to fire after the relocation if they fail their save.
• If placed in a choke point between you and a group of enemies that must move to engage you it can slow their approach and give you time to prepare. It also has the benefit of having a chance of consuming an action giving you even more time.