/usr/share/help/sl/gpl/index.docbook is in gnome-desktop3-data 3.28.1-1ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/help/sl/gpl/../../../help-langpack/sl/gpl/index.docbook
/usr/share/help/sl/gpl/../../../help-langpack/sl/gpl/index.docbook