/usr/include/libsyncml-1.0/libsyncml/ is in libsyncml-dev 0.5.4-2.1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/libsyncml-1.0/libsyncml/data_sync_api/
/usr/include/libsyncml-1.0/libsyncml/data_sync_api/callbacks.h
/usr/include/libsyncml-1.0/libsyncml/data_sync_api/defines.h
/usr/include/libsyncml-1.0/libsyncml/data_sync_api/standard.h
/usr/include/libsyncml-1.0/libsyncml/sml_auth.h
/usr/include/libsyncml-1.0/libsyncml/sml_base64.h
/usr/include/libsyncml-1.0/libsyncml/sml_command.h
/usr/include/libsyncml-1.0/libsyncml/sml_defines.h
/usr/include/libsyncml-1.0/libsyncml/sml_devinf.h
/usr/include/libsyncml-1.0/libsyncml/sml_devinf_obj.h
/usr/include/libsyncml-1.0/libsyncml/sml_ds_server.h
/usr/include/libsyncml-1.0/libsyncml/sml_elements.h
/usr/include/libsyncml-1.0/libsyncml/sml_error.h
/usr/include/libsyncml-1.0/libsyncml/sml_manager.h
/usr/include/libsyncml-1.0/libsyncml/sml_md5.h
/usr/include/libsyncml-1.0/libsyncml/sml_notification.h
/usr/include/libsyncml-1.0/libsyncml/sml_parse.h
/usr/include/libsyncml-1.0/libsyncml/sml_session.h
/usr/include/libsyncml-1.0/libsyncml/sml_transport.h
/usr/include/libsyncml-1.0/libsyncml/syncml.h