What does the interviewer mean when he asks what key technologies have you worked on?
Basically, "key technologies" mean the important stuff that people watching the news actually care about; the bread that makes the baker money.
When asking about "Key competencies", the interviewer simply wants to know the personal abilities you have that enable you to apply technical skills (either learned at the company, or previously). Key competencies are typically things like: Promlem Solving, Working with others and in teams, Collection and Analysis of information, Communicating ideas and information, Using technology, Planning and Organizing, and Using mathematical ideas and concepts.
I'm assuming you mean from a student's perspective? Answer the questions honestly. Try to back up your answers with solid thinking and good facts. If the interviewer asks you, "why do you want to go to Harvard?" don't just say "Because it's Harvard," or "the campus is really pretty"! Let the interviewer know who you are. And don't worry, they aren't out to get you...they really want to see you succeed and get in! Also…