What is the ruling on shrouding and burying, or gifting to a medical student, or selling and donating the proceeds to him, a human skeleton that was used for study?

It is not permissible to sell a human being or a part of one, as they are not owned. However, it is permissible to use a human corpse or skeleton for a recognized legitimate purpose. There is no objection to transferring it to someone who will benefit from it for the same purpose. If it is no longer needed, then if it belongs to a Muslim, it should be washed, shrouded, and prayed over. If it belongs to a Dhīmmī, it should be shrouded and buried. If it belongs to neither, it should be buried to prevent harm.