How many green onions are in a bunch?
Well, I can at least show you what ALDI in Germany considers a bunch:





It weighs about 200g and if I wrap my hand around it, my finger touches the middle joint of my thumb, which according to JBergen's comment, makes it a medium bunch.

And in this bunch are....

Seven onions!

But the exact number is probably not really important. Cooking can be a pretty exact science occasionally, but most of the time, a bit more or less won't make or break a recipe. So use common sense and the 7 onions / 200g per medium bunch as a guideline. If your onions are especially pungent, you might want to cut back, if they are mild or you want a bit of a punch, be more generous.