Postgres 9.6

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
create table tab ( js jsonb );

CREATE TABLE

insert into tab values
('["UserMailer", "applicant_setup_3", ["5cbffeb7-8d5e-4b52-a475-3cf320b2cee9"]]'),
('[{"reference_id": "5cbffeb7-8d5e-4b52-a475-3cf320b2cee9", "job_dictionary": ["StatusUpdater", "FollowTwitterUsersJob"]}]');

INSERT 0 2

select * from tab;

js

["UserMailer", "applicant_setup_3", ["5cbffeb7-8d5e-4b52-a475-3cf320b2cee9"]]

[{"reference_id": "5cbffeb7-8d5e-4b52-a475-3cf320b2cee9", "job_dictionary": ["StatusUpdater", "FollowTwitterUsersJob"]}]

SELECT 2

    select jsonb_array_elements(js) as elm
      from tab
      
elm

"UserMailer"

"applicant_setup_3"

["5cbffeb7-8d5e-4b52-a475-3cf320b2cee9"]

{"reference_id": "5cbffeb7-8d5e-4b52-a475-3cf320b2cee9", "job_dictionary": ["StatusUpdater", "FollowTwitterUsersJob"]}

SELECT 4

select q.elm
  from
  (
    select jsonb_array_elements(js) as elm
      from tab
  ) q
 where elm::varchar like '%User%';
 
elm

"UserMailer"

{"reference_id": "5cbffeb7-8d5e-4b52-a475-3cf320b2cee9", "job_dictionary": ["StatusUpdater", "FollowTwitterUsersJob"]}

SELECT 2