Your uncle's lawyer friend might not be able to do anything for your admission to Penn, especially if he's not your assigned interviewer. Is he someone that's well-connected to Penn (other than just being a graduate)?
If he's just a non-active alumni, then I wouldn't go so far as to prepare questions and a transcript. Just meet with him (I would say business casual is fine) over coffee and ask him about what his experiences were like at Penn, as a courtesy more than anything else. If you leave a really good impression on him, maybe he'll write a note to admissions, but again, unless he has some pull in the Penn community, I wouldn't think that would be very consequential.