You need to know your stuff particularly you need to be very slick on the CRP-5 and the other weak area is understanding variation & deviation and being able to apply CDMVT in both directions. Gyro wander is part of instruments and OP and not GN.
There will be some theory questions like great circle definitions along with some obtuse questions you can memorise but other than that knowledge and lots of practice is the key.
I would agree that passing GN by QB alone will not work, however they are really useful for seeing how the questions are asked which is not necessarily how it's presented in course material. After I have taught a GN topic I recommend the students to use QBs for practice and understanding the questions which is half the battle.
Good tips Phil and the recommendation!