What is the ruling concerning money found in a used shoe that was gifted to someone, and does the ruling differ if the original owner is unknown?

This money is considered a Luqatah (found item). The finder is the one who found it, not the one who gifted the shoe. He is obligated to announce it for a year, during which he searches for its owner. If he finds the owner, he returns the money to him. If he does not find the owner, the money becomes the property of the finder.

If the buyer finds money in an animal he purchased, such as a sheep or a fish, it is considered Luqatah for him, and he is obligated to announce it, starting with the seller.

If he catches a fish and finds an unperforated pearl in its belly, it belongs to him. If he sells it unknowingly, his ownership is not relinquished, so it should be returned to him.

However, if the fisherman finds something in the fish's belly that could only belong to a human, such as dirhams, dinars, or a perforated pearl, it is considered Luqatah. If the fish's buyer finds it, the responsibility for announcing it falls upon him.

If there is no hope of finding the owner of the Luqatah, then according to some scholars, announcing it is not obligatory.