Edit: didn't quite read close enough this morning...
Anyway, I would just ask him or her questions about their experience, and ask for advice. If they're agreeing to meet you, they can probably anticipate most of what you'll ask. Ask about how they ended up practicing in the area of law they're in, how they got their first job out of school, and things along that line. You can also ask for any advice they have about law school, your job search, interviewing with firms, etc.