Third, create a folder for working on ruby stuff in.
So ‘in’ is a preposition, and requires an object. So it’s either implied, or it’s earlier in the sentence.
A guess is that ‘folder’ is the object. I don’t think there are other good objects.
I didn’t find an easy rewrite. This sentence doesn’t seem to fit the pattern of some sentences which end with prepositions that have easy rewrites like “What did you say that for?” which would become “For what did you say that?”
A rewrite I did was “Third, create a folder in which to work on ruby stuff”. “for” is dropped and “working” changes to “to work”. Th rewrite kind of indicates to me that “folder” is the object I’m looking for.
Here is how that tree would look:
It seems super clunky but it doesn’t seem like nonsense. It kinda makes sense that it would be clunky though because there is a reason it’s not actually used like that: to avoid the clunkiness.