Thread title.
I'm allowing a player to add the Steel-Breaker Brawler's and the Martial Artist Monk's Exploit Weakness together, but perhaps this is actually canon.
Channel Energy: If I have this ability from more than one class, do they stack?
No—unless an ability specifically says it stacks with similar abilities (such as an assassin's sneak attack), or adds in some way based on the character's total class levels (such as improved uncanny dodge), the abilities don't stack and you have to use them separately. Therefore, cleric channeling doesn't stack with paladin channeling, necromancer channeling, oracle of life channeling, and so on.
/cevah