Well, that gets a little complicated, but here's a quick swing at some of the various ratings:
Bridge Crew Ratings:
Gunner: Gunnery/Spacecraft, Sensor Operations, Communications/Conventional
Quartermaster: Navigation/Space, Sensor Operations, Computer
Sensor Operator: Sensor Operations, Communications/Conventional, Computer
Sensor Technician: Sensor Operations, Computer, Technician/Electronics
Communications Technician: Communications/Conventional, Computer, Technician/Electronics
Weapons Technician: Technician/Weapons, Technician/Electronics, Computer
And other possible combinations...
Engineering Ratings:
Nuclear Technician: Technician/Nuclear, Technician/Jets, Computer
Hull Technician: Technician/Mechanical, Technician/Aeronautics, Computer
Electrical Technician: Technician/Aeronautics, Technician/Electronics, Computer
Thruster Technician: Technician/Jets, Technician/Aeronautics, Computer
And many other possible combinations...
"Deck" Ratings:
Bosun's Mates: Technician/Mechanical, Communications/Conventional, Navigation/Space
"Top Men" (work on Jump Sails): Technician/Myomer, Communications/Conventional, Navigation/Space
And other possible combinations...