Sorry this is long, but here is my two cents for you!
I have a little technical trouble shooting experience, but not much. I worked myself up and was very nervous because I'm not sure what to do if someone drops their laptop or spills soda all over their phone. I'm great at customer service though, and that's what they loved about me.
The approach I took was explaining how I would respond to the specific technical situation -- being very empathetic and polite. I also explained how I would do anything I could to help bring the situation to a happy resolution.
That's the approach I took with all the technical questions. I only had about 2.. the first interview seemed much more customer service oriented. The second one touched on what I had done at my past jobs and how I would respond to a situation like stated above.. like if someone dropped their computer and was really upset.
I've realized everyone's interview is completely different. Some have two.. some have three.. some seem more customer service oriented (like mine) while some get some deep tech questions. It seems to vary based on how the interview is going. Every person I spoke with was very laid back and very nice. It was the most comfortable interview I have ever done (to my great surprise) in that the recruiters and team leaders were very easy to talk to.
I'll say don't worry, but I know that's easier said than done. I drove my family CRAZY through this interview process with my nerves and stress. Just have a happy, confident tone and things will go great. Answer questions to the best of your ability, and if you don't know the answer, explain what you would do.. like research to find a solution to resolve the customers concerns.
I think they're really looking for people who have a great phone voice and attitude.. Someone that will be great with customers. Someone that is willing to and wants to learn... Someone that will utilize their tools available to them to help the customer as much as possible. Someone that completely understands empathy and how to talk to people in upsetting situations. If you can do this, you have nothing to worry about at all. That's exactly what I did and who I am!
To more specifically answer though.. I have seen where people have been asked about how to navigate the Apple website, I was asked about some basic functions on my phone (I have an iPhone) and asked about iTunes. I think they just try to gauge how comfortable and familiar you are with the products or if you're willing and eager to learn and familiarize yourself. To prepare, I spent some time playing around on the website, but I ended up not being asked anything about it. It helps to prepare though. It helped me feel more confident and ready. So play with your/someone's iPhone or iPod, touch an iPad (even a display in a store) and try to go somewhere and play with a Mac on display (like Best Buy) just to get yourself a little more familiar before the second interview. Just some ideas since I don't know what they may throw your way!