/usr/share/sounds/ubuntustudio/stereo/system-ready.ogg is in ubuntustudio-sounds 0.10.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/sounds/ubuntustudio/stereo/dialog-question.ogg
/usr/share/sounds/ubuntustudio/stereo/dialog-question.ogg