/usr/share/doc/libplot-dev/changelog.Debian.gz is in libplot-dev 2.6-2ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libplot-dev/../libplot2c2/changelog.Debian.gz
/usr/share/doc/libplot-dev/../libplot2c2/changelog.Debian.gz