I usually just read them and thought about them a little. It depends on the prof, though... is she likely to ask you those questions outright? Does she not care in the slightest what the author of the casebook thinks about anything and is using it for the actual case opinions only?
I personally think a few lines of case notes is the way to go, but I still prepared differently for classes, again, according to the prof. This mainly had to do with how closely I read and whether I could do a whole week's reading over the weekend to be ahead of the game or whether I really needed to wait until the night before, to keep details fresh in my mind.