You measure the resistance of the load (speaker) in ohms, then run a constant test tone and measure AC volts. The current is your voltage measured divided by the resistance.
I prefer any product made by fluke, they hold there specifications, typically other branded meters will require alignments after 12-16 months to maintain their specs. FYI, I have calibrated that very Extech clamp meter shown in video. Those are defiantly junk and have seen them fail right out of the box.