How many calories should a 9 year old lose?

That depends on your weight and height. Do some research on something called 'caloric deficit'. That is how you will lose weight. The more calories you cut, the more likely you are to lose more weight, but you have to exercise at least 40-60 minutes a day, getting no exercise won't help at all.

To be completely honest with you, losing a pound a day is practically starving yourself. I was once thinking like that when I was 12, but I'm 15 now and I think differently about things. But hey, feel free to do research, and most likely you wouldn't want to talk to your doctor about what your doing about the weight loss, although they may tell through a blood test result... Most likely blood sugar will drop, and blood pressure will drop. This is something you need to do a lot of research on, this could turn into an eating disorder which can lead to anorexia. Good luck on losing weight. But please, be very careful, losing 1 pound per day is difficult and can be dangerous. Take my advice and go a little more slowly.