for example i have a student table with (studentid) i want to get a list of triggers that use this field...
for example if in table X there is a trigger that uses studentid i want it to be shown in the query result.
You can do that by querying pg_proc and pg_trigger,
SELECT t.tgname FROM pg_trigger t, pg_proc p
WHERE t.tgfoid=p.oid AND p.prosrc like '%studentid%';
If you want to filter on the tablle name if you have too many triggers just add a filter on relname from pg_class
SELECT tgrelid::regclass,t.tgname FROM pg_trigger t, pg_proc p, pg_class c
WHERE c.oid = t.tgrelid AND t.tgfoid=p.oid
AND c.relkind = 'r'
AND p.prosrc LIKE '%studentid%' AND c.relname = 'X';