Values are usually printed on the front of the brown wafer, but they're only visible when you remove them from the bass.
They could be labelled as 100KA (100kΩ, Logarithmic sweep), but occasionally you'll get one that doesn't, at that point you'll have to desolder it from the wiring (after first labelling or some other means of identifying how to put it back - ask me how I found this out!) and measuring it. It's not generally a good idea to measure the value of components whilst they're soldered on place, as they can often be wired with other passive components (fixed resistors, diodes and capacitors) that can skew the reading.