its a snap ring and its hidden inside the joint.
Put the shaft in a vice, with the joint angled downwards, get a lump of metal, i use a blunt cold chisel, and place it against the inner most part of the CV (theres the outer shell, a cage with some balls, then an inner hub) and give it a good hard smack and it should pop off. Have someone handy to catch the joint.
Mashing randomly at it with a soft hammer wont do anything. The impact all needs to go into the inner hub, at as shallow an angle as possible, and it needs to be a sharp, hard, hit.