I would say you can choose from any of the other characters you have created so like if you're a hunter and you have both warlock and titan you could take voidwalker/sunsinger/defender or striker. But if you only had one other character then you could only take from whatever that one has. and it can only be "taken" from the character if you have it maxed out. I mean by now you should have all of them maxed out but just saying. And i put taken in " because it's not that the character you took this from loses it's it'd be like replicating it on your hunter.