If you're looking for "proof" that CM Punk is racist you won't find it, assuming proof is "I hate black people" or "kill all n1ggers". Anyone in 2012 working for any kind of reputable company is smart enough to behave reasonably well in public. For a white person to broadcast explicit racism in 2012 would take outright idiocy or being high/drunk, and Punk doesn't drink or do drugs.
This doesn't mean it doesn't exist. CM Punk was seething with rage over Chris Brown's generic responses to him on twitter, leading to him challenging CB to a fight and fantasizing about "curb stomping" him... a concept most people are only familiar with because of American History X. This is just one of many incidents.
Then you look at his friends/idols. Chael Sonnen, a good pal of his. Roddy Piper, who loathes and is disgusted by black people, his youth wrestling idol.
If you're looking for a smoking gun or admission, you won't find it, but there are many more racists than those that are "proven" with explicit statements. You have to go on more subtle reasonings/comments and patterns, and with CM Punk it is an endless occurence.