/usr/share/man/man2/mq_notify.2.gz is in manpages-dev 3.74-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/man/man2/../man3/mq_notify.3.gz
/usr/share/man/man2/../man3/mq_notify.3.gz