Tracking power feed short to switch

[diygiy]

120v household line. Feed line suddenly lost power. Tenant reports no heavy usage at the time - says she just finished a shower so possible condensation/steam issue caused the short. one gfci in bathroom works fine, no load on gfci just a direct 12-3 yellow feed line into gfci no load out (appears only bathroom is on bathroom circuit breaker). Double switch box is the problem - first switch controls bathroom fan and shower light. Second switch controls vanity light. Seems main power feed from the "wall" is dead (tested with volt meter and main feed line to switch box is dead). No other outlets or switches seem to be on bathroom breaker (all other outlets & switches in apartment work)

I have a few options to get power to the switch box - but my question is how best to track the short in the line? AFAIKnow, since gfci works, energizing from the breaker side will tell me know more than i know now. Is cutting sheetrock the only sure way to track the short location? I would try looking for lower resistance but only the gfci and the double switch seem to be on the circuit. Any suggestions i appreciate - thank for taking time to read my post

 

[Reach4]

Some things are unclear to me. You refer to a "Double switch box" as the problem. Does that mean a 4 inch wide box with two separate switches? The fan and the light controlled by the switch work fine, or do one or both not work?

You say "no load on gfci just a direct 12-3 yellow feed line into gfci no load out". Where is that gfci, in a separate box?

What relationship does the gfci have to the "Double switch box"? They are just on the same breaker?