I would choose this guy in my old class who acted really mean and dumb but was also obviously really smart. Everything he did was like a show for us and I would like to know what he actually felt and thought inside.

Good question!

Someone in my immediate family. You'd think I'd be able to tell by now, but nope, their minds are still shrouded in mystery. I would want to know anything and everything that crosses their minds, what interesting things they know, what makes sense to them and how they figure things out.