/usr/lib/x86_64-linux-gnu/tkConfig.sh is in tk-dev 8.6.0+8.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/tk8.6/tkConfig.sh
/usr/lib/x86_64-linux-gnu/tk8.6/tkConfig.sh