How much sugar is in watermelon? If you made fresh, pure watermelon juice, how many calories per 8 oz, or per 12 oz, would it be?

Shouldn't matter. Watermelon is 92% water, and only 8 % "other things". In other words, the calorie count is negligible. Weight watchers considers watermelon to be a "free food", meaning you could eat an entire watermelon and not count any points. They are high in lycopene, a nutrient good for the heart, and have some natural fiber. So enjoy!
Not important. What is important is that watermelon juice is quite dirrerent from eating the fruit. This is because the fiber in all fruit plays a vital part in how the fruit sugar is absorbed and processed. The juice by itself is just a dilute sugar solution. You never find sugar in a free state in nature. It is always wrapped up in a fruit, a stem or a root and that is the way that god intended us to get it.
CALORIES. Watermelon is mostly water and less sugar compared to grape or other fruits.Eat as much as you want and don't worry about the calories, you just increase your fluid intake by eating them.