/usr/share/doc/libonig-dev/README.ja.gz is in libonig-dev 5.9.1-1ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libonig-dev/../libonig2/README.ja.gz
/usr/share/doc/libonig-dev/../libonig2/README.ja.gz