Apply input voltage difference between true and complement of +1V and apply 3V at output. Then measure current sink inside the circuit. This will give IOH
Similarly apply negative input voltage and supply a 6mA current to the output pin, and measure the voltage on output node. This will give VOL.
From application diagram this is only nmos driven and you cannot drive a high voltage from this circuit. So VOH cannot be defined here. But IOL can be defined for this circuit for a particular voltage driven at the output.