Galaxy workflow and history structure is stored in Galaxy's database vs. flat files so you can't just find the representation of those on the file system.
I actually don't know if there is any documentation about the JSON structure for those artifacts - I've CC'd the -dev mailing list so someone there might know (btw, emailing the -dev list is preferred with questions like these because your question get more exposure). In the mean time, you can explore the API documentation (available
here and
here) because that's where JSON objects can be retrieved.