Where does apostrophe go with a noun such as sheep eg The vet is attending to all the sheeps feet?

The answer depends on whether you are talking about one sheep, or several sheep. If there is only one sheep and the vet is attending to all its feet, you would say: "The vet is attending to all the sheep's feet." If there is more than one sheep, however, you would say "the vet is attending to all the sheeps' feet."