/usr/src/linux-headers-4.4.0-66-lowlatency/sound is in linux-headers-4.4.0-66-lowlatency 4.4.0-66.87.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/src/linux-headers-4.4.0-66-lowlatency/../linux-headers-4.4.0-66/sound