Depends on the experience level of the interviewee. If they are fresh out of school I expect them to know algorithms and data structures and maybe some specific topic they studied at an advanced level (like compilers, db, graphics, etc). If they are 5-10 years into a career, they should have a lot of knowledge about whatever it is they've been doing. If someone says they have 5 years of Android programming, I'm going to ask them a lot of Android API questions as well as Java.

In either case, there are questions that have multiple difficulties of responses. The more experienced/capable they are, the more nuanced and complete their answers will be. For example, ask a Java person how GC actually works. Most people have very little idea, but the best talent knows a good bit more.

But there are other variables. I've known perfectly intelligent and productive coders who took months to build a really complex well architected system that didn't solve the business problem and hence were a bad hire.