/usr/share/xsessions/ubuntustudio.desktop is in ubuntustudio-default-settings 0.54.
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 8 | [Desktop Entry]
Version=1.0
Name=Ubuntu Studio Session
Comment=Use this session to run Ubuntu Studio as your desktop environment
Exec=startxfce4
Icon=
Type=Application
Name[en_US]=ubuntustudio
|