/usr/src/xtables-addons-3.0/extensions/pknock/Mbuild is in xtables-addons-dkms 3.0-0.1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | # -*- Makefile -*-
obj-${build_pknock} += libxt_pknock.so
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