What position, junior designer? Mid-level? Creative? Is this in a studio, or for a business that have an in-house team?
Ultimately I suspect they'll be asking about your approach to work, how you came up with X idea in your portfolio, techniques used, how up to date you are with technology/software/techniques, as well as wanting to know a little about you as a person. Be honest, and don't be afraid to admit you don't know something if you don't. Studios typically have someone or several someones that fulfil specific roles, such as artworking for example. If you're not an artworker (or whatever), don't claim to be, it will just bite you in the arse when you mess up a huge print order.
People hire people, so don't be afraid to just be yourself. Even if you're not exactly what they're looking for, if you come across as a nice person who can fit into their team straight away, you might get in. Good luck!