I'm trying to find out how to set JPEG only mode on my Canon 5D Mark II - which options do I need to set from which menus?
Assuming you mean a 5D MK II (spelt with a capital i not a 1), Menu -> "first tab" (in red) -> Quality -> shutter wheel to set RAW to "none" and aperture wheel to set JEPG. (Must have on button in the correct place, might work with the joystick too.)
BUT I would HIGHLY recommend to always shoot RAW. Some groups apparently need the fast JPEG (e.g. photojournalists at sports events) but even in that case I would suggest you obtain a RAW file which you can edit later on.