What are the most common difficult interview questions?

It's different for everyone. The basics of an interview is that you introduce yourself and them to you. Then they ask you some questions, usually prepreparred and they ask everyone the same questions. Then they ask if you have any questions. It's a good idea to have a few. If they answer all your questions, tell them no, they answered all of them for you. Then it's usually over and they call you back in a few days or not.