How to trace wiring?

[stevet]

(DIY here). Bathroom outlet, above sink, has no power. Measured resistance between neutral and ground, about 20 ohms. Probably open hot wire (black). Bathroom also has 3 switch's, 2 lights, one fan. All 3 switch's work. No loose wires in the either box. The bathroom outlet has black and white wires on the top and bottom of the outlet, probably feed from somewhere else. I forgot to check jumpers on the outlet. My question is , how to find the other electrical box that feeds this outlet ? Fox and hound ? I opened outlet boxes in living room, and kitchen ( walls close to the bathroom wall). The outlets where pulled out and tested with fluke 88, set to AC on high range (probed the wires). Circuit breaker panel removed, tested each breaker output with meter, all where good. House is about 50 years old. Do not want to open every electrical box in the house to look for loose/poor connections. Thank you.

 

[westward10]

Has a GFCI tripped somewhere and did it work previously.

 

[stevet]

Has a GFCI tripped somewhere and did it work previously.

Only one GFI in the house, it has not tripped. The bathroom outlet worked previously. Went through the house checked for switches that did nothing, couldn't find anything.