if you short your drain and gate and apply an idea current source in drain, you will be able to measure your kn knowing the current you set and VGS and Vt can be found by "printing DC operating point"
for nmos it is about 380 uA/V^2
for pmos it is about 80 uA/V^2
note that the method which i proposed ignore the channel lenght modulation, so for small current (eg 50uA), you will have a higher kn to compensate your channel length modulation which increases the current.