Seriously – no one was told how to do it?
It works (I’m only ever chopping 2-3 onions max mind, but can’t see how more would be a problem).
pull roots off but leave the root stump attached.
chop the pointy/leafy bit off.
Chop onion in half from top to bottom (through the root stump).
Peel the outer dried layers off and the first kinda moist/fresh/tough one that you wouldn’t really want to eat.
slice the onion from the bottom to the top, but not through the stump (so point of knife in near the stump and cut up to what was the pointy bit).
Do this at an angle to make cuts like a terry’s chocolate orange, although you can do straight but older onions will get a big flap wobbling about when you do the next stage.
Turn onion 90 degrees and either chop course or fine.
done.