MySQL Using AND Statement
FLIGHTS.destination_citycannot be the same value at the same time, therefore a join of the same table for each destination reference is required like:

SELECT f1.source_city
FROM FLIGHTS f1
JOIN FLIGHTS f2 ON f1.source_city = f2.source_city
WHERE f1.destination_city = 'Honolulu'
  AND f2.destination_city = 'Newark'
 ;