/usr/lib/x86_64-linux-gnu/libjacknet.so is in libjack-jackd2-dev 1.9.9.5+20130622git7de15e7a-1ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libjacknet.so.0.1.0
/usr/lib/x86_64-linux-gnu/libjacknet.so.0.1.0