RPG

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. I don't think that is too much to ask of a player at all considering how much smoother and more fun it makes the games.

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.