Unlike the 34901A module, the 16-channel 34902A module does not include a dedicated current measuring channel.
Instead, add a user-supplied shunt resistor to the circuit and use a scaling equation to convert the voltage drop across the shunt to mA or the engineering units of choice. This same technique can be used to measure current on the non-dedicated current channels of the 34901A.
The shunt resistor should be a low-value, high-precision resistor, placed in series with the circuit-under-test. Power dissipation and drift characteristics in the shunt should be considered. Accurately measure the resistance of the shunt so that a precise scaling factor can be calculated using Ohm's Law.
The link below is a video demonstrating this technique of using a shunt resistor to measure current on a voltage channel.