Hi @wisemanleo
I’d say the most effecitve route really depends on how your data is progressing through the workflow. Do you already have a json as input and you want to modify it or do you have something table based and want to create a nested structure from there? I assume the latter since I see Column and Table to JSON node’s in your screenshot. Something is slightly off though because your current input shows an opening array which is not closed of.
If would be possible to enrich your post with the workflow or an (anonymized) data set that is the input for your JSON, you are more likely to get someone to jump in and have a go at it 
A similar use case is discussed here: