abs

Combine resistance training with cardio for best gains.
It's possible in two weeks, but only if your ab muscles are already decently built. To get a six pack you need two things. A low body fat percentage and some muscle. Cardio will only help to reveal what muscle is already underneath the fat layer (for the most part). You need to make sure you don't over-do cardio because this will cause muscle wasting, meaning less abs (and muscle in general) and fattening in the long term (because of a decreased metabolism with muscle loss).

The best thing to do would be combine resistance/strength training along with the cardio (not necessarily at the same time/day). This will give you the best improvement. Two weeks won't be enough time for resistance training to build up your abs much (probably not noticeable), but it will at least prevent the muscle from wasting away along with fat from the cardio exercises.