The rules are quite clear: the only prereq is knowledge (any) 5 ranks. There is no prereq of having a domain, nor having a divine based class. The general rules about the domain type feats are given on page 52. The basic idea is that in order to take one, you either have to believe in a deity that has that portfolio option, or believe in the principles related to said domain, if the character does not believe in a deity listed. You still have to follow alignment and theme restrictions. As I mentioned, there are no class or class feature requirements.