Session:

    dbus-send --session --type=method_call --print-reply --dest=org.freedesktop.DBus /org/freedesktop/DBus org.freedesktop.DBus.ListNames

System:

    dbus-send --system --type=method_call --print-reply --dest=org.freedesktop.DBus /org/freedesktop/DBus org.freedesktop.DBus.ListNames

You can also use [DFeet][1] if you prefer a GUI tool.


  [1]: https://live.gnome.org/DFeet/