/usr/include/owncloudsync/ is in libowncloudsync-dev 1.7.0~beta1+really1.6.4+dfsg-1+deb8u1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/owncloudsync/creds/
/usr/include/owncloudsync/creds/abstractcredentials.h
/usr/include/owncloudsync/creds/httpcredentials.h
/usr/include/owncloudsync/mirall/
/usr/include/owncloudsync/mirall/account.h
/usr/include/owncloudsync/mirall/folder.h
/usr/include/owncloudsync/mirall/folderman.h
/usr/include/owncloudsync/mirall/folderwatcher.h
/usr/include/owncloudsync/mirall/mirallconfigfile.h
/usr/include/owncloudsync/mirall/networkjobs.h
/usr/include/owncloudsync/mirall/progressdispatcher.h
/usr/include/owncloudsync/mirall/syncengine.h
/usr/include/owncloudsync/mirall/syncfileitem.h
/usr/include/owncloudsync/mirall/syncjournaldb.h
/usr/include/owncloudsync/mirall/syncresult.h