In his first appearance in the episode “Cancer Man”, Ken mentions a number of what sound like firms, one of which he claims would “make (him) partner” just for walking in the door". Later, he suggests a bonus for himself which is “less than 10% of what I billed last quarter”. Sounds like a lawyer to me.
But next time we see him later in the episode, he talks about having a better attorney than someone he’s in a dispute with.
The Breaking Bad wiki says he’s a “businessman”.