If you want to estimate it, you use the coefficient of friction to determine the friction forces wherever there are two components moving one against the other, then you build a free body diagram to find the resultant force/torque.
If you want to measure it, you move the elevator at constant speed and measure the force required to maintain that motion. It should be equal to the friction force. If you measure the power instead of the force, then you have to divide by the speed of the elevator to find the force.