I use this in my `~/.jq` when I have a problem like this.

    def flat_json_keys:
        [leaf_paths as $path | {"key": $path | map(if (type=="string") then (if (test("([?:\\W]+)")) then "['"+.+"']"  else . end) else "["+tostring+"]" end) | join(".") | gsub(".\\[";"[") , "value": getpath($path)}] | from_entries;

    def ukeys:
        keys_unsorted;

Use like so:

    cat wat.json | jq flat_json_keys