Most likely they will ask about the most common gof patterns used by
j2ee. So I sincerely doubt they will ask about flyweigth or interpreter.
What you also have to realize is that they will not go into patterns details, implementations, etc. They'll give you a J2EE element and ask you what GoF pattern it implements, or vice versa.
The design patterns is one of the easy part and you get 2-3 questions on it, no more.