I was looking over the Sneak Attack entries in D&D 4th Edition, as I am playing a rogue in a Planescape campaign. Anywho, I was wondering if a Short Sword +2 would add it's enhancement bonus to Sneak Attack damage, as well as the AB and the normal damage roll.
Sneak attack is extra damage added to the attack. It's part of the attack roll where the enhancement bonus is already added, you don't get to add it again.
So you should have:
Attack: 2 (ENH) + Dex + 1/2 lev + 2 (CA) + x (other mods)
Damage: 2 (ENH) + Dex + Sneak Attack + x (other mods)
For most of your powers.
As a commenter points out, because this damage is part of the attack roll, it's maxed on a critical hit as well (this also goes for other striker damage like the warlock's curse, and ranger's quarry dice).
You would add the bonus to your damage. However, you would only add it once.
Bonuses that are different types will stack - therefore, the Sneak Attack damage bonus will stack with the ability score bonus and the enhancement bonus. Your overall damage for a sneak attack will therefore be
[Weapon damage] + [Sneak attack damage] + [Enhancement bonus] + [Ability score bonus]
If you have or get other modifiers later on, you can add them too.