There's no telling what they may ask you but just be yourself, greet them with a firm handshake, be personable, establish eye contact, and be honest. Honesty is very important because they need to feel that they can trust you- even if it involves admitting a mistake. Try to show them that you are someone who knows how to read and interpret technical material and that you really want to learn. They know you are a new A&P and that you have a "License to Learn". Don't act like you already know it all because you don't and they know it.
Equally important is how you dress for this interview. DON'T WEAR A COAT AND TIE!! If they see you dressed like that they will assume that you want to push a pencil or drive a desk and that's not what they're looking for. They are looking for bright, rugged guys who aren't afraid to get dirty in gearwells and hellholes. Wear a clean and pressed Western-style work shirt with some clean and pressed boot-cut jeans and some nice boots or leather shoes. Dress like a workin' guy.
They want people who they feel will work hard and learn and grow with their company and the best start for that is for them to like you right up front. First impressions are everything here.
This is a tough business. The pay is pretty low for what it is and there is little union support in lots of areas. You'll find forklift mechanics making lots more money. If you're like me, though, aviation will be the only thing that you can stay focused on long enough for it to be a career for you. Good luck to you!
I appreciate JetDoc voting me up and he makes a real good point about learning what you can about the company before the interview. I do, however, stand by my advice on what you wear. You could go with dark brown Dockers instead of jeans. I've been part of a number of hiring teams and everybody always seemed to gravitate toward mechanics who arrived clean and well-groomed but looked like they were really ready to get to work. If we needed mechanics and a young guy showed up looking like a supervisor he probably wouldn't get the nod over the other "Workin' Guys". Now, if we were hiring supervisors or inspectors, we might tend to focus more on guys who fit that image.