They aren't going to ask you to talk about compression and turbine stages.
They will ask you questions relevant to your flying experience and involvement in aviation.
I would say if you don't have any flying experience, then try and have atleast a BAK type level before heading in.
If you have a PPL, then somewhere along the lines of a CPL level type theoretical knowledge should be sufficient.
They might ask you a couple of questions that go beyond your level, but that could be anything, and don't be afraid to say you don't know.
Study and understand the basics before moving on. Studying the compression and turbine stages of a GE90 when you have absolutely no clue about the fundamentals is pointless and if the interviewer continually asked ATPL and type specific questions then they need a kick in the ass.
Use a bit of common sense.