/usr/lib/tk8.6/tkConfig.sh is in tk8.6-dev 8.6.1-3ubuntu2.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
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#! /bin/sh . /usr/lib/`dpkg-architecture -qDEB_HOST_MULTIARCH`/tk8.6/tkConfig.sh