Ham hocks give a special mouth feel to soups and stews, in addition to its smoky flavor. The hock is the joint between the leg and foot of a pig... the pig's ankle, in other words. It contains a lot of tendons and other connective tissue, which will add fat and collagen to a dish. This results in an almost silky consistency.
Ham hocks may not be readily available in your area. I've found them at Walmart, so check your local store. Or go to your favorite search engine and enter "ham hocks near me" and you might find some local butcher shops that carry them.
I've found that one of the best substitutes for ham hocks is a ham bone, especially from a smoked ham. If you had a bone-in ham for a holiday dinner, you can definitely use the bone (with any attached meat) in a soup or stew. Bone marrow also contains fat, collagen, and more vitamins and minerals than meat, including glucosamine—a compound that can help with joint pain and inflammation. So bone marrow will help five your dish some of that silky feel, and also provide some health benefits.
If you can't find ham hocks at all, you can another smoked meat. Ham, smoked sausage, smoked bacon, or smoked turkey legs will all work. but none of them will give you the same mouth feel as ham hocks.