What can be done for someone in a coma; does he hear or feel what is around him, and where is his soul?

There is no impediment to treating an afflicted colleague with legal ruqyah (definition) using the Quran and supplications, for it has been authentically reported that the Prophet, peace and blessings be upon him, used to perform ruqyah on himself and his companions. As for the question "Where is his soul?" if you mean its location within the body, this is part of the knowledge of the unseen which Allah has reserved for Himself. If you mean whether it has left his body, then he is in the ruling of one who has fainted, and his soul leaves him just as the soul of a sleeper departs.