It looks like there are current-measuring resistors on the cathodes of the power tubes. It's those little brownish resistors that connect to the standoffs right next to the sockets. They should connect to pins 1 and 8 on the power tube sockets. If they are the common 1ohm resistors then 1mV measured across that resistor equals 1mA of current (for that tube only). You'll also need to measure the plate voltage on the power tubes (pin 3).
If you want to measure the actual bias voltage you can measure that at pin 5 or on that PPIMV on the outside lug that has the resistor soldered to it. Or back at bias supply on the board. You can measure that with the amp on Standby but it often changes a tiny bit once the amp is ON.
You can measure the value of those cathode resistors on the power tubes by measuring across them with the amp OFF and unplugged, make sure they are 1ohm before you do any calculations. Just make sure you switch your meter back to 'voltage' before doing the other measurements.
One of those adjustment pots is to adjust the range of the bias supply (to use different tube types usually) and the other is for the typical adjustments once you've decided what tube type you want. Usually you would adjust the one that has one lug connected to ground (most likely the one closest to front of amp) but in reality you can use either one.
Cool amp!