There’s a lot of literature on Eskimo Song Dueling up through the 1920’s. How it worked:
Luke feels slandered by me. He believes I have said that he is a terrible fisherman and his children go hungry.
At a meeting of our village he calls me out.
Everyone forms a circle, and we start singing. The two of us take turns hurling evidence/insults for our prosecution/defense.
“The verses are earthy and very much to the point: they are intended to humiliate, and no physical deformity, personal shame or family trouble is sacred.”*
He sings that I am unable to satisfy my wife.
I sing that he smells like a seal carcass left out for a week.
We take turns and the crowd cheers between exchanges.
The duel ends when a) one party is satisfied they have been heard out, or b) one party loses their voice and cannot continue, or c) the community, by consensus, cheers the winner and drowns out the loser.
This is how criminal and civil matters were settled, up to murder. Is there a need for a particular new Mannish skill for this, or can this be handled with Forks of Ugly Truth and Singing?
Man’s Rise to Civilisation – Peter Farb (London: Secker & Warburg, 1969)
If it was going to be a significant part of one culture in your setting I’d make it its own skill for the same reason that dwarves have stuff like Stentorious Debate - because it’s going to be more effective in their culture and not effective in other people’s culture, and an outsider won’t necessarily be able to jump right in. A Greek philosopher suddenly forced to debate with dwarves in front of a dwarven audience will be shouted down and flustered, but a dwarf shouting himself purple in front of the Athenian forum will just convince everyone he’s a boor.
I’d probably use Sing as the body of argument skill–being able to sing for a long time lets you stay in it. Heck, maybe have it take the place of Will. Actual actions would use the base social skills or an appropriate custom set, -Wises that are allowed to FoRK and FoRKs are a bit broader. Have a few character traits that are voice/song related that count for BoA and you are golden.