/usr/share/tcltk/tk8.6/demos is in tk8.6-doc 8.6.1-3ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/tcltk/tk8.6/../../doc/tk8.6-doc/demos
/usr/share/tcltk/tk8.6/../../doc/tk8.6-doc/demos