Force Oracle to return TOP N rows with SKIP LOCKED

“From what I have seen, Oracle applies the WHERE predicate before determining what rows to skip.”

Yup. It is the only possible way. You can’t skip a row from a resultset until you have determined the resultset.

The answer is simply not to limit the number of rows returned by the SELECT statement. You can still use the FIRST_ROWS_n hints to direct the optimizer that you won’t be grabbing the full data set.

The software calling the SELECT should only select the first n rows. In PL/SQL, it would be

DECLARE
  CURSOR c_1 IS  
    SELECT /*+FIRST_ROWS_1*/ qt.ID
    FROM QueueTest qt
    WHERE Locked IS NULL
    ORDER BY PRIORITY
    FOR UPDATE SKIP LOCKED;
BEGIN
  OPEN c_1;
  FETCH c_1 into ....
  IF c_1%FOUND THEN
     ...
  END IF;
  CLOSE c_1;
END;