how can I see what's inside descriptors.jsondb?

The easiest way to examine the contents of descriptors.jsondb is with vscript:

$ vscript
> o = sg.list_descriptors();
  [object Object]
> print(sg.to_json__pretty_print(o));
  {
    "veracity" :
    {
            "path_parent_dir" : "C:/Users/iolsen/AppData/Local/.sgcloset/repo",
            "repo_id" : "gfbe4f5b8d02f41d0b0ced0c5e77322a582338db6413311e0945660fb42f09aca",
            "admin_id" : "gdb4b04002a44462ab6d3da25ec2d7ebc82337574413311e0945660fb42f09aca",
            "storage" : "fs3",
            "dir_name" : "veracity_4f2f"
    },
    "veracity_hosting" :
    {
            "path_parent_dir" : "C:/Users/iolsen/AppData/Local/.sgcloset/repo",
            "repo_id" : "g13d107db7c37443db1cb348e3568c7eae0edbd60d89e11e09639001cc0372cb0",
            "admin_id" : "gdb4b04002a44462ab6d3da25ec2d7ebc82337574413311e0945660fb42f09aca",
            "storage" : "fs3",
            "dir_name" : "veracity_beae"
    },
    "veracity_test" :
    {
            "path_parent_dir" : "C:/Users/iolsen/AppData/Local/.sgcloset/repo",
            "repo_id" : "gd550402f456543279933c1c4f0a452949b485bf9ac3511e0b40f1c6f65d71da9",
            "admin_id" : "gdb4b04002a44462ab6d3da25ec2d7ebc82337574413311e0945660fb42f09aca",
            "storage" : "fs3",
            "dir_name" : "veracity_95dc"
    }
  }

You can get this same information for a single repository using vv:

> vv repo info veracity --verbose
  Repository:           veracity
  Default push/pull:    http://bits.ad.sourcegear.com/repos/veracity

  Descriptor:
  {
    "path_parent_dir" : "C:/Users/iolsen/AppData/Local/.sgcloset/repo",
    "repo_id" : "gfbe4f5b8d02f41d0b0ced0c5e77322a582338db6413311e0945660fb42f09aca",
    "admin_id" : "gdb4b04002a44462ab6d3da25ec2d7ebc82337574413311e0945660fb42f09aca",
    "storage" : "fs3",
    "dir_name" : "veracity_4f2f"
  }
  ...

If you wanted to drop down one layer of abstraction, a jsondb file is a sqlite3 database, so you could also poke around in it with sqlite3 tools.