I'd ask just enough to see if the person really knows C# and move on to more important questions. Start with simple stuff like what the main method looks like, what data types are available, and basic class functionality. :)
I really don't think you can answer this question accurately. Last month I went on at least 10 different interviews, and I came up with 10 different interviews.
Some people will ask more about your work ethic, or about previous projects. Others will grill you with technical questions about object-oriented programming. Some will try to trip you up with trick questions about different .NET library tools. I even had one ask if I preferred tea or coffee as a genuine interview question!
So really, it depends. I think the best advice is just to know you, and know what to do. Further, don't be afraid to say you don't know something, but also be sure to indicate an understanding of a concept if they explain further.