power to the diode you can't really measure easily without dismantling things. You need a multimeter to read voltage and amps. voltage*amps = Watts, a unit of power.
Measuring laser power takes a power meter. They are general expensive though. A half decent name brand setup will run you $400 and a decent name brand setup will run you into the 4 figures. You can get lesser meters for $100+. In any case, if you just have a single laser to measure you may want to pay the shipping to send it to someone else who can measure it for you.