[Sundraoi]

I believe it's charisma with modifiers for both notoriety and the NPC's reaction. So they can contribute indirectly by scoring success on using the skill in conversation.

Last I checked, it's listed somewhere in the server features.

It's a combination of Charisma modifier, Wisdom modifier, and Notoriety. I do not believe it mentioned skills.

EDIT: The NPC's opinion of the player also comes into play.

Persuasion has a big effect on the opinion of NPCs towards your PCs