/usr/include/groonga/ is in libgroonga-dev 6.0.1-1ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/groonga/groonga/
/usr/include/groonga/groonga.h
/usr/include/groonga/groonga/array.h
/usr/include/groonga/groonga/command.h
/usr/include/groonga/groonga/config.h
/usr/include/groonga/groonga/dat.h
/usr/include/groonga/groonga/dump.h
/usr/include/groonga/groonga/expr.h
/usr/include/groonga/groonga/file_reader.h
/usr/include/groonga/groonga/geo.h
/usr/include/groonga/groonga/groonga.h
/usr/include/groonga/groonga/hash.h
/usr/include/groonga/groonga/ii.h
/usr/include/groonga/groonga/nfkc.h
/usr/include/groonga/groonga/normalizer.h
/usr/include/groonga/groonga/obj.h
/usr/include/groonga/groonga/output.h
/usr/include/groonga/groonga/pat.h
/usr/include/groonga/groonga/plugin.h
/usr/include/groonga/groonga/portability.h
/usr/include/groonga/groonga/request_canceler.h
/usr/include/groonga/groonga/scorer.h
/usr/include/groonga/groonga/thread.h
/usr/include/groonga/groonga/token.h
/usr/include/groonga/groonga/token_filter.h
/usr/include/groonga/groonga/tokenizer.h
/usr/include/groonga/groonga/type.h
/usr/include/groonga/groonga/util.h
/usr/include/groonga/groonga/windows.h
/usr/include/groonga/groonga/windows_event_logger.h