/usr/sbin/grub-mknetdir is in grub-ieee1275 1.99-21ubuntu3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/sbin/../lib/grub/i386-ieee1275/grub-mknetdir
/usr/sbin/../lib/grub/i386-ieee1275/grub-mknetdir