You can use the following to list the triggers and see what functions they call. Then you can check pg_proc to see how TRUNCATE is used in prosrc.
SELECT c.relname,
t.tgname,
p.proname AS function_called,
t.tgconstraint AS is_constraint,
CASE WHEN t.tgconstrrelid > 0
THEN (SELECT relname
FROM pg_class
WHERE oid = t.tgconstrrelid)
ELSE ''
END AS constr_tbl,
t.tgenabled
FROM pg_trigger t
INNER JOIN pg_proc p ON ( p.oid = t.tgfoid)
INNER JOIN pg_class c ON (c.oid = t.tgrelid)
WHERE tgname NOT LIKE 'pg_%'
AND tgname NOT LIKE 'RI_%' -- < comment out to see constraints
-- AND t.tgenabled = FALSE
ORDER BY 1;