It's an incomplete quote, so here's the context: "Sometimes, who we wish we were, what we wish we could do -- it's just not meant to be." (from Disney's "Moana") So what we desire might not always become reality. Of course, the heroine of the film showed us otherwise. :)

It's hard to say since there's not much context, but I'll try. "Who we wish we were" = "What kind of person we want to be or become" "What we wish we could do" = "The things that we want to be able to do"