Where is the camshaft position sensor on a 99 Saturn SC2 and how do you replace it?

A camshaft position sensor does not exist on a 1.9L Saturn of any kind. It is simply a code the ECU whips up when there is a problem somewhere in the ignition. Could be anything from spark plugs to where it all begins. I would start by checking your spark plugs, then wires, then coils, then the module the coils sit on, and any connections in between. Should find the problem, but sometimes it can be more complicated.