After removing an old tub 40 years old. Discovered two yellow wires.
Is there a way to check voltage with the covering on the wires. Unable to track where they go?

They look low voltage. I'd cut one and test it and tape it back with electrical tape if it tests.

Purchase a voltage sensor, about $15.

That should tell you whether you have voltage on the line. Assuming you find voltage begin turning off breakers, that will tell you what devices are on that circuit. With that information you should be able to logically figure out where the lines run from and to.

Be aware that both lines may not be on the same circuit.