/usr/include/python3.6dm/sip.h is in python3-sip-dev 4.19.7+dfsg-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/include/python3.6dm/../python3.6m/sip.h
/usr/include/python3.6dm/../python3.6m/sip.h