If there is a manufacturer's name and part number on the pot, you can get that information from the web site. You can also use a meter and observe the change in resistance over a few degrees at either end of travel. A log taper will show much more change in resistance at one end than the other.
Another quick check is that when you set the potentiometer to the approximate midpoint, the two resistances will be pretty nearly the same value if the pot is linear.