/usr/lib/unity-settings-daemon-1.0/gtk-modules/canberra-gtk3-module.desktop is in libcanberra-gtk3-module 0.30-0ubuntu3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 | [GTK Module]
Name=canberra-gtk-module
Description=Event Sound Module
X-GTK-Module-Name=canberra-gtk-module
X-GTK-Module-Enabled-Schema=org.gnome.desktop.sound
X-GTK-Module-Enabled-Key=event-sounds
|