/usr/bin/gtk-update-icon-cache is in libgtk2.0-bin 2.24.10-0ubuntu6.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/bin/../lib/x86_64-linux-gnu/libgtk2.0-0/gtk-update-icon-cache
/usr/bin/../lib/x86_64-linux-gnu/libgtk2.0-0/gtk-update-icon-cache