World-of-warcraft – How to find your logs in worldoflogs

Yes, you can. Before Wrath of the Lich King was released, the only way to enchant someone else's gear was to have them place it in a trade window -- which meant you couldn't use an enchanter alt to put enchantments on your main character's gear, and selling enchantments involved advertising in trade chat and meeting people face-to-face. (The horror!)

WotLK (via the Inscription profession) added enchanting vellum, which an enchanter can place an enchantment on to "store" it for later use. You can then send it to your alt or even list it on the auction house. To use it you just right click it like you would a scroll, then click on the gear you want to enchant.

Yes, you need to use a dagger if you want the bonus damage. Unless otherwise stated, all Rogue abilities use the weapon in your mainhand.

The only two that break from this are Mutilate (uses both hands, simultaneously) and Shiv (which uses only the off-hand)

But -- You're barking up the wrong tree if you're thinking Daggers will cause more damage than other weapons - daggers are unique in having a different (i.e., lower) damage bonus for instant attacks (this is why you don't want to Sinister Strike with a dagger - it'll do less damage than an equivalent iLvl sword, mace, or axe).

Ambush used to be dagger specific. When the ability was updated to be more useful to other specs, they had to do something to make sure ambush wasn't suddenly worst for the dagger specs, hence the extra bonus.

This constant is called the Normalized Weapon speed. WoWpedia has more.