lets say a zoo/aquarium is preparing a new stingray touch tank that is around 10,000 gallon tank (35 feet in length) how many adult cownose ray can it fit to that tank? I think 10 cownose ray or less can fit there
You can certainly fit ten. Quite a few more would be possible, depending on what else is in the tank (both animal and decoration-wise).
Well width and depth play an important part as well, but in a tank that size you could fit quite a few! I had a breeding group of 7 in a tank ~1200 gallons, and they did quite fine in there. In a tank with 35 feet of straight travel, assuming its at least 6-7 feet wide, you could house 30+ adult rays comfortably. Also @FelipeDBKO, a fish keeping form will be nigh on useless for this question. Very, very, VERY few people keep pelagic ray species privately, and of those who do, they often only house 1 or 2 juvenile specimens in systems that would not be able to handle groups of adults, so are perhaps not the best sources of advice for stocking densities.
@yousuf89 This is a zoo fan group. Many of the members are teenagers. For the well being of your (theoretical) animals, do not look here for technical advice. Much of the information you will receive is just inexperienced people wanting to be helpful. If this is a game that is one thing. If you really want technical advice, contact a respectable aquarium that keeps the animals. They'll very likely be happy to assist. Certainly there are professionals in the UAE who could advise.