I have submitted a snap titania, which requires dbus access to de.create3000.titania, because it is Gtk::Application application. I defined a slot a follows:
slots:
dbus-titania:
interface: dbus
bus: session
name: de.create3000.titania
de.create3000.titania is my own app id, you could also have a look at http://create3000.de/.
Thank you very much for your help!
Holger Seelig