What is the best and fastest wotkout or exercise to burn belly fat?

Hard to do: It is very difficult to decrease fat in only one part of your body. Obviously core related exercises such as certain types of sit-ups will tone the muscles in the belly and make them look less fat and losing weight overall will also decrease the fat in the belly as it does everywhere else. Know your body as to where fat comes and goes first.

Abdominal fat: Abdominal fat increases with stress and cortisol along with Insulin and sugar. I will suggest that patients eat right as starving stresses the body and raises cortisol. Exercise at smaller intervals or interval training instead of endurance. Eat a lower glycemic diet (no necessarily low carbohydrate) lots of veggies and enough healthy fat in the diet. Reduce stress in the lifestyle.