We only dived at two locations in Jamaica on our way along the north coast.
Montego Bay. This is a busy cruise port and there are plenty of shallow snorkeling sites off the airport plus a few deeper dive sites with moorings. There are also a few more moorings south of the port. There is a Conservation Center at the most easterly harbor that has a map of dive sites.
Negril. We tried one dive only in this bay on the west end of Jamaica. There were a lot more moorings there we would have liked to explore.