Just check that the MM probes are plugged into the right sockets. There's normally two sockets for the red/positive probe, one for voltage and resistance, and another for current measurements. Normally only one for the black/common probe. It's easy enough to plug in to the wrong socket by mistake and get no readings.
If that's fine, you could always test the multimeter resistance across the two outer legs of a potentiometer. You know that's going to be close to the nominal pot value - 250k or 500k - and this value is not affected by being an audio or linear pot.