They can come from the front or rear legs, though usually from the front.
If they come from the rear legs of the pig, they’re called “ham hocks”, but you treat them the same.
There is a lot of bone, gristle and connective tissue in them. At both ends, you’ll see the cross-section of a round bone — that’s the shank bone.
They are sometimes sold fresh, sometimes smoked or cured.
Cook by braising or simmering in a stew, etc.
When you’re cooking pork hocks as part of a dish, you remove them from the dish when the meat is cooked and tender, use a fork to get the meat off, put the meat back in the dish, then discard the bone and gristle.
In the American south, pork hocks are often braised. Then towards the end of cooking, collard greens are added to the pot.
Substitutes
A ham bone with ham left on it