Baldur's Gate : The Sword Coast Chronicles : NWN2 Persistent World

So I know this ability only triggers on one attack. But what about your off hand? Does that count as a new trigger?

Also, does it get bonus from the daggerspell mage spell damage?

Only triggers once per round. So if your main hand attack misses and your secondary hits, that's when it'll trigger.

It's not a ranged touch attack so it shouldn't gain bonus dmg from Daggerspell Mage.