I am currently remodeling my bathroom. Home built in the 50's with existing knob and tube. Bathroom has power coming into 1 switch that controls lighted medicine cabinet with outlet inside cabinet. Want to add 1 new light fixture, 1 GFI, and 1 ceiling fan (no light). Is there any diagram that would be helpful. What about grounding? It looks like there is a ground connected to existing box for medicine cabinet. Can I use this? Any help would be much appreciated.

Check with your Authority having jurisdiction (Example electrical inspector). Each area has a different set of rules when dealing with K&T. Personally, I would run a new circuit and wire to today's code!