/usr/lib/x86_64-linux-gnu/libk3blib.so is in libk3b-dev 17.12.3-0ubuntu3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libk3blib.so.7
/usr/lib/x86_64-linux-gnu/libk3blib.so.7