Your buddy has an exhaust gas sensor installed on him? And you want to check it?
When I check the O2 voltages in real time (car running), I simply gain access to the O2 signal wire for the side I'm testing. This can be done in the kick panel where the EEC harness connects to the computer or at the O2's connector. If doing the latter, I'd recommend a jumper harness so you are not lying underneath an idling car. The kick panel might be the easiest.
Put the meter on the scale that encompasses one volt (often 5 volts) and watch the meter. It should quickly go from ~0.05 to 1.0 volts (+/- a little bit) at least once a second, if not faster.