/usr/share/xsessions/gnome-xmonad.desktop is in xmonad 0.11-6build1.
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 7 | [Desktop Entry]
Name=GNOME with Xmonad
Comment=A GNOME fallback mode session using xmonad as the window manager.
Exec=gnome-session-xmonad
TryExec=gnome-session
Icon=
Type=Application
|