You can do this using the INFORMATION_SCHEMA tables as well as the system catalog.
http://www.alberton.info/postgresql_meta_info.html
eg.
List Sequences
SELECT relname
FROM pg_class
WHERE relkind = 'S'
AND relnamespace IN (
SELECT oid
FROM pg_namespace
WHERE nspname NOT LIKE 'pg_%'
AND nspname != 'information_schema'
);
Trigger list
SELECT trg.tgname AS trigger_name
FROM pg_trigger trg, pg_class tbl
WHERE trg.tgrelid = tbl.oid
AND tbl.relname !~ '^pg_';
SELECT tgname AS trigger_name
FROM pg_trigger
WHERE tgname !~ '^pg_';
SELECT DISTINCT trigger_name
FROM information_schema.triggers
WHERE trigger_schema NOT IN
('pg_catalog', 'information_schema');
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