Where is the submarines sickbay?

Submarines don't have a sickbay per se (i.e., a medical ward) since there aren't any doctors aboard. Essentially, the ship's Corpsman (usually a First Class or Chief Petty Officer), works out of a small equipment space (still called sickbay though) that's not much bigger than a closet. In general, it's located either adjacent to or near the ship's mess deck. This is due to the fact that for emergency surgery, the wardroom table can be converted to an operating table, and during a shipwide casualty with major injuries, the mess hall can be converted to a first aid/casualty station. The mess deck is also usually centrally located in the forward section of the boat.