You'll be unable to measure the motor directly as its a 3 phase brushless DC motor. You can measure the current draw from the battery using a WattsUp meter or the device d8veh shows in his pic above. Be aware though that this is the current draw from the battery it does not tell you the current the motor is actually using due to the way the controller and BLDC motors work. Also keep in mind there is some loss in the controller itself and the motor is not 100% efficient. At peak current draw from the battery which normally coincides when climbing a hill at half top speed this efficiency drops to around 65% or lower, the loss being turned into heat in the motor and controller.
