some sort of elm... need help

[Poink88]

Where should I chop this tree in spring? I was thinking keeping both trunks the thicker on the left a bit taller than the thinner one.

Or do two airlayers and make brooms. And keep the original lower trunk, cut the right thinnner branch to create some taper.

Depends on your taste. Me, I'll chop as marked.

 

[barrosinc]

Yeah kinda like that was what I was thinking, maybe a tiny bit higher. Are you thinking leaving the tree much higher with a new leader to build taper??
I might stick the long cutting in the ground to see if they root and make a brrom.

 

[Poink88]

I will keep it as I marked (maybe even shorter) to have room to build the new leader and taper.

Usual mistake I see is failure to visualize the trunk chop area plus the new top (rest of trunk plus branches and ramification) above it.

Depending on the base, trunk & branch, tree species, target bonsai style, etc., I usually shoot to chop anywhere from 1/3 to 2/3 of the target finished tree. There are exceptions but that is the normal guideline I follow for most.

Very personal approach & preference I am sharing which may fit your style or not.