little help please
The single 14-2 comes from one of the receptacles. It is a 2-wire loop. Open receptacles until you find it. When you do, you will find that one wire in the 14-2 will be wired to the hot circuit of the receptacle, and the other wil come back from the switch and wire to the switched side.
You will have to rewire that receptacle in order to get a neutral over to your light switch. Usually, the switch is at the end of the run since it is a 2-wire loop. So, you probably have a 14-2 from the switch and a 14-3 to the rest of the receptacles in that box. Wire the red and black from the 14-3 to the black from the 14-2, and the brass screw on the receptacle. Wire the whites together and the silver screw on the receptacle. Now the 14-2 at the switch will be hot and neutral. You just get your can light wire down and wire white to white and the blacks on the switch.