I wouldn’t require players to read the whole rulebook or books. However I expect players to know the basic rules that come up all the time after a while. Also I expect players to know what their spells and abilities do and have the page numbers noted on their character sheet/pdf/whatever next to the ability for easy referencing. This is something I make very clear during session zero. There is some learning by doing and there is some reading up you need to do.

In return players can expect me to know all the rules which I expect to be relevant during a session (e.g. if there will likely be underwater combat I’ll make sure I refresh my knowledge on that). As a GM I will make sure I know the spells and abilities of all enemies and monsters I use and how they might interact with the PCs. I’ll also have page numbers for rules, spells and monsters ready if things get unclear.