/usr/lib/slepcdir/3.1/include/finclude/ is in libslepc3.1-dev 3.1-p6.dfsg-1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/slepcdir/3.1/include/finclude/slepc.h
/usr/lib/slepcdir/3.1/include/finclude/slepc.h90
/usr/lib/slepcdir/3.1/include/finclude/slepcdef.h
/usr/lib/slepcdir/3.1/include/finclude/slepceps.h
/usr/lib/slepcdir/3.1/include/finclude/slepceps.h90
/usr/lib/slepcdir/3.1/include/finclude/slepcepsdef.h
/usr/lib/slepcdir/3.1/include/finclude/slepcip.h
/usr/lib/slepcdir/3.1/include/finclude/slepcip.h90
/usr/lib/slepcdir/3.1/include/finclude/slepcipdef.h
/usr/lib/slepcdir/3.1/include/finclude/slepcqep.h
/usr/lib/slepcdir/3.1/include/finclude/slepcqep.h90
/usr/lib/slepcdir/3.1/include/finclude/slepcqepdef.h
/usr/lib/slepcdir/3.1/include/finclude/slepcst.h
/usr/lib/slepcdir/3.1/include/finclude/slepcst.h90
/usr/lib/slepcdir/3.1/include/finclude/slepcstdef.h
/usr/lib/slepcdir/3.1/include/finclude/slepcsvd.h
/usr/lib/slepcdir/3.1/include/finclude/slepcsvd.h90
/usr/lib/slepcdir/3.1/include/finclude/slepcsvddef.h
/usr/lib/slepcdir/3.1/include/finclude/slepcsys.h