Hes asking for a good ab workout, not how low bodyfat should be to see them.
My ab routine..
Russian Twists, Leg raises on the tower or hanging on the chin up bar, ball abdominal crunches, weight crunches (cable machine crunches or just plain machine)
Core lifts should be included, Deadlifts, squats, lunges & planks ( 1 hand, 1 leg ) on leg day..
Turkish getups are really good too, but i cant do them lol!!