Użyj ->> operator
:
-- Example data
create table test (id int, js jsonb);
insert into test values
(1, '{"a":"1","b":"2","c":"3"}'),
(2, '{"a":"1","b":"2","c":"4"}');
--query
select *
from test
where js->>'c' = '3';
id | js
----+--------------------------------
1 | {"a": "1", "b": "2", "c": "3"}
(1 row)
