I would add to what the others said:
In the real world, no one knows everything (although some folks act like they do). I would advocate to learn well how to use your electronics to do the things you need to do on every flight. You should be able to do them without having to think about how to. Things like reset your altimeter, tune a radio, find a frequency, understand what's on the map, know what those numbers on the PFD mean, go direct to somewhere, and set a speed bug. Also, know what common alerts and warnings mean. The things about your EFIS that are deeper into the weeds you need to have read at least once so you at least have a feel for where to find it later on, but they cannot expect you to know everything. A flight examiner will expect you to safely fly using the instruments that are installed in your plane. The basics of how things work are fair game, but he won't expect you to know specifics of how to install or repair the system.
Ken