Good question! Here's a sample agenda we put together that provides an outline for just that. Sessions are most valuable when you show up engaged, with an idea of what you'd like to get out of your time with your mentor.
We strongly recommend that you come prepared to each session with a clear outline of topics you'd like to cover—perhaps notes about questions that came up during the week, specific projects you'd like to look at, or design topics you'd like more guidance on. Have fun!