How to generates VALUES literal expression using a query?
Are you looking for this:
WITH foobar(foo, bar) AS (
  VALUES
  (1::integer,'a'::text),
  (2,'b'),
  (3,'c'),
  (4,'d')
)
SELECT format('(%s, %L),', foo, bar) FROM foobar;

  format   
-----------
 (1, 'a'),
 (2, 'b'),
 (3, 'c'),
 (4, 'd'),
(4 rows)