You should be able to speak to your process - how you begin an User Experience/IA project, how you proceed through discovery into documentation, what kind of documentation you like to use and your process around that, you should be able to discuss how you work through challenges with tough clients, challenging PMs, and unforseen situations that arise. Talk about how you like to work - self-managed, or very collaboratively co-authoring all your docs? You should be prepared to discuss all the docs in your portfolio - how you arrived at solutions that your sitemaps and wireframes illustrate. Also talk about your philosophies around User Experience and IA. Its nice to know you actually have thought about how your role fits into the whole interactive development team.