knucklebone is essentially the knee (joint) and femur & shin are the thick, straight leg bones, with or without the joint at the end.
here are some photos, unfortunately all these bones are smoked (ie, cooked) so NOT a good choice, you want raw, fresh, and still holding some scraps of tasty meat and not greasy carcinogens and artificial flavor!
cut femur bone:
intact femur bone:
knucklebone:
