/usr/share/tcltk/tk8.5/demos is in tk8.5-doc 8.5.19-1ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/tcltk/tk8.5/../../doc/tk8.5-doc/demos
/usr/share/tcltk/tk8.5/../../doc/tk8.5-doc/demos