KNOB AND TUBE,,, no ****? This is the wiring with glass insulators, and bare wires that are attached to the insulators and run through floor joists inside ceramic tubes. IF this is what you have,,,, don't run anything on it.... and get it replaced.... it is an increased fire hazard to the building, and most insurance companies will not even insure this anymore.
Now,,, if it is just plain jane 2 conductor BX wiring or something,,, you can run a ground wire. But knob and tube is too dicey for this. A rodent can cross the legs, old glass tube fail,,,you name it. If you have real, for gosh, knob and tube wiring,,,,, run a new circuit, even if it is just for one recepticle.