Folder/file ownership: API https://api.dropboxapi.com/2/sharing/list_folder_members

Using /2/sharing/list_folder_members[/continue] is the correct way to look up the owner of a shared folder. The member who owns the shared folder, if any, would be identified by the "access_type" value being "owner" (in place of "editor" in your sample).

In your output, there isn't an owner listed though. This, along with the lack of the option on the web site, can be because the shared folder is in your "team space", meaning that it's owned by the team itself, as opposed to any specific member. So, team admins can manage this folder, but you can't transfer ownership to specific individuals.