The only ones you should be really worried about are for the commonly given medications. There aren't that many of them. Digitoxin, digoxin, gentamycin, vancomycin and dilantin are the ones I've seen tested for the most. It's very unlikely you'll get asked about obscure things. When you are in your clinical sites, ask different nurses and unit secretaries what therapeutic levels they are seeing ordered. You'll hear the same ones coming up again and again. Those are the ones you should know for sure. That should narrow your list down considerably.
NCLEX questions generally come from nurses and are reviewed by nurses before they make it to the exam. They are not going to put questions on there to purposely see if you were reading the small print in your books. When they ask questions about drugs or medications you can almost always be sure they have come out of the background of nurses who have worked with them in their clinical areas, so they will be commonly used or ordered medications. Not something off the wall.