/usr/include/postgresql/9.5/server/replication/ is in postgresql-server-dev-9.5 9.5.2-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/postgresql/9.5/server/replication/basebackup.h
/usr/include/postgresql/9.5/server/replication/decode.h
/usr/include/postgresql/9.5/server/replication/logical.h
/usr/include/postgresql/9.5/server/replication/logicalfuncs.h
/usr/include/postgresql/9.5/server/replication/origin.h
/usr/include/postgresql/9.5/server/replication/output_plugin.h
/usr/include/postgresql/9.5/server/replication/reorderbuffer.h
/usr/include/postgresql/9.5/server/replication/slot.h
/usr/include/postgresql/9.5/server/replication/snapbuild.h
/usr/include/postgresql/9.5/server/replication/syncrep.h
/usr/include/postgresql/9.5/server/replication/walreceiver.h
/usr/include/postgresql/9.5/server/replication/walsender.h
/usr/include/postgresql/9.5/server/replication/walsender_private.h