/usr/include/postgresql/9.5/server/commands/ 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/commands/alter.h
/usr/include/postgresql/9.5/server/commands/async.h
/usr/include/postgresql/9.5/server/commands/cluster.h
/usr/include/postgresql/9.5/server/commands/collationcmds.h
/usr/include/postgresql/9.5/server/commands/comment.h
/usr/include/postgresql/9.5/server/commands/conversioncmds.h
/usr/include/postgresql/9.5/server/commands/copy.h
/usr/include/postgresql/9.5/server/commands/createas.h
/usr/include/postgresql/9.5/server/commands/dbcommands.h
/usr/include/postgresql/9.5/server/commands/dbcommands_xlog.h
/usr/include/postgresql/9.5/server/commands/defrem.h
/usr/include/postgresql/9.5/server/commands/discard.h
/usr/include/postgresql/9.5/server/commands/event_trigger.h
/usr/include/postgresql/9.5/server/commands/explain.h
/usr/include/postgresql/9.5/server/commands/extension.h
/usr/include/postgresql/9.5/server/commands/lockcmds.h
/usr/include/postgresql/9.5/server/commands/matview.h
/usr/include/postgresql/9.5/server/commands/policy.h
/usr/include/postgresql/9.5/server/commands/portalcmds.h
/usr/include/postgresql/9.5/server/commands/prepare.h
/usr/include/postgresql/9.5/server/commands/proclang.h
/usr/include/postgresql/9.5/server/commands/schemacmds.h
/usr/include/postgresql/9.5/server/commands/seclabel.h
/usr/include/postgresql/9.5/server/commands/sequence.h
/usr/include/postgresql/9.5/server/commands/tablecmds.h
/usr/include/postgresql/9.5/server/commands/tablespace.h
/usr/include/postgresql/9.5/server/commands/trigger.h
/usr/include/postgresql/9.5/server/commands/typecmds.h
/usr/include/postgresql/9.5/server/commands/user.h
/usr/include/postgresql/9.5/server/commands/vacuum.h
/usr/include/postgresql/9.5/server/commands/variable.h
/usr/include/postgresql/9.5/server/commands/view.h