Knowledge is broken into a bunch of subskills, so trivia would most likely have specialties -- i.e. Trivia (20 C humor) -- to cover the particular area. For an 'entertainer' character that was played, Entertain: Singing (Jazz); another was Entertain: SEx Acts (we would give the specialty here...)
With skills, I pretty much go with the credo, 'if it's not in the rules, make it up'.
"War is an ugly thing but not the ugliest of things; the decayed and degraded state of moral and patriotic feelings which thinks that nothing is worth war is much worse. A man who has nothing for which he is willing to fight, nothing which is more important than his own personal safety, is a miserable creature and has no chance of being free unless made and kept so by the exertions of better men than himself."
John Stuart Mill