Solving for electromotive force constant in motor armature circuit
If you are using SI units, the Ke constant is both the back EMF constant (describes how many volts per rad/s ) as well as the torque constant of the motor, ie how many N-m of torque you get per Amp of armature current. So you can solve for it with the stall current and stall torque given in the data sheet: Ke = 0.5932N-m / 5A = 0.119 N-m/A.  It's a good exercise to convince yourself that the units are actually the same as V/s^-1.