Sorry I can't anticipate what they might ask you, but I can provide you some general advice for interviews...
Don't forget, this is a 2-way exchange, not an interrogation. I think a lot of people walk into an interview with the mindset that they are there to do whatever it takes to convince the company of their worth, and talk along the lines of "begging" the benevolent company to grant them the opportunity to work there, even if in the cold dark gear locker. It's understandable to feel this way, especially if you have been out of a job for a while. But know your worth. No need to beg. No need to lower yourself for them. You are there to interview them, as much as they are there to interview you. Are they worthy of having you? Ask questions about the company to determine if it's even some place you would like to see yourself working. If you are competent in the field you're applying for, act like it. The confidence you display will do more for you than the words that come out of your mouth. (but don't overdo it and be "****y")
If you're not competent for what you're applying for; if you're fresh out of school and it's an "entry-level" position then be more humble, but still don't beg.
And everything is negotiable. If they go to the effort of extending you an offer letter, it means you have something they want. So recognize that, and get the best deal you can up front. Don't settle for something less than what you need, in hopes of getting a raise later, because it will not likely happen. Every raise you get, is based on what you were making before, so if you start low, there will be a cumulative error by the time you retire that could be >$1M. If the dollar amount is fair, then take it. Maybe ask for some other benefits, like stock options or a modified schedule. When I took my current job I accepted the dollar amount but negotiated for the title that I wanted, and for a 4-day work week.