As I've mentioned several times, I've had the pleasure to interview many applicants in my present and past jobs and I've always diverted to the "less used" list of questions that are located somewhere in my brain. It's down pack and set - that if you have used any of these "less used" features of C#, you've definitely been around or at least done some digging.
Not that these are really required for day to day development, however, it proves that you are experienced and have some love for the game. It proves that you go home and code, research and keep yourself up to date. The pace in which technology is moving these days, one has to be on top of it or you will be left behind. Anyway, here are my favorites and if you don't know them, please take some time to learn what they are and how they can be used - its a challenge!
The readonly keyword modifier.
Question: What is the different between the const keyword and the readonly keyword?
The volatile keyword.
Question: Can the volatile keyword be applied to a value type field?
Question: Is volatile interchangeable with lock?
The checked keyword.
The fixed statement.
Question: Can you use the fixed statement in a safe context.
The yield keyword.
Question: Can it be used in an anonymous method?
The :: Operator
Indexers
The internal access modifier.
Have Fun!