the tranny pan drain plug is remove with the car level (on ground is tight but doable), running, in park, and with an ATF temp of something like 87F. I forget the exact number, but it is usually checked via VCDS. You can use a IR thermometer on the pan, but not sure how close it will be.
There should be a red plastic "stand pipe" up inside the drain hole. it is removed with an Allen wrench if you want to drain the fluid for a change, not for checking the level. It sticks up inside the pan a couple inches and is open at the top, allowing ATF to overflow into it and drain through the drain port. The volume the ATF takes up is highly dependent on temp, so that is why it is measured at a specific temp. What that means is the ATF level in the pan is that much higher than the bottom. Make sure it is there, but don't remove it unless you are changing fluid.