[Renate]

I've updated the Leaf1-2.png (the "map" diagram).
There's the test points near the LED connector marked "Danger".
Don't mess with them at all. (It's only ~20V but it could burn something up or burn itself out).

Stage one:

Get a piece of paper to keep track of your results.
With the device plugged into USB and the black probe measuring off that nice bit of tin on the WiFi/BT module measure some voltages.

With your DVM (the yellow looks nice) in DC volts mode:
You're looking for one spot measuring 1.8V and the adjacent spot measuring near 0 (like <0.1).
Mark them down on paper and notate which were zero volts.
If something measures over 1.8V, like 3.3 or 5V it's nothing that you want.
When you're done, did you get any suspicions?

Step two:

Time to try stuff. Put your meter in the diode mode (blue triangle bar)
Black to tin.
Now you pick a likely zero voltage point and measure.
If it says 0.0 (or close) it's just a ground point.
If it say OL, it's probably not what you want. (but might be worth checking later if you get nothing)
If it says numbers, that's a possibility.
With the probe held on the spot, do a long >10 second power push and see if something shows up on USB, like 9008.

Theory: The diode test puts out a safe voltage and current which we can use to trigger the EDL (if it's the right pin). Except for that LED area you're not going to break anything.

Just to reiterate:
You can measure voltage on any (non-LED) point in stage one.
Only do diode test in stage 2 on things that you've already measured as zero-ish.