/usr/lib/x86_64-linux-gnu/libjack.so is in libjack-dev 1:0.125.0-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libjack.so.0.0.28
/usr/lib/x86_64-linux-gnu/libjack.so.0.0.28