dexterity is a simple addon.
If you have 30,000 dexterity and the tooltip says .3x dex it does an additional 9,000 damage due to dex. *this is why people who say to stack dex because of the modifiers are idiots. the damage gained is so low. This is why we stick to stacking physical attack instead of shit like dex/stam*
[30,000] x [.3] = 9,000
That's all that is.
So it would be:
End of skill damage (with the forumla) + 9,000 [which is the additional dexterity damage] = total damage
Dagger level (weapon level in general) increases accuracy per weapon.