If nothing else, have an idea of the kind of places each particular plane goes to, i.e short haul or long haul. That is all I got asked on the multi choice test but some of the other guys/gals on my course have told me they got asked more specific questions.
My advice would be to learn whatever information NATs send you, it will be useful, if not at the selection day then at the interview. Also when you are at the college you will have to learn data for 50 aircraft, so you mays well start now!!!
Also I can recommend Air Traffic Control by Graham Duke. This book cost me about 7GBP on Ebay and helped get me through my interview.
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