Abs show depending on your level of bodyfat. If you want your abs to show, the #1 thing to do is lower your bodyfat as long as you don't have problems with loose skin after losing a lot of weight.
You can work your abs to build the muscle which only takes you so far. Not very far at all actually unless you're trying to bulk your ab muscles which will make your stomach stick out. No matter how much you build them though, if there's too much bodyfat, that can cover them up completely.
Also, one more thing to note, if you're trying to reduce bodyfat of just your ab area to make them show, you're doing it wrong. You can't really spot reduce bodyfat, your body stores it as it's programmed and burns it the same.
