And where would this online court be operating from? Who are the judges answerable to? Who will pay them? Who will select them? From which particular law does its existence spring forth?

This is a complicated matter because legal jurisdictions are limited. You cannot just create an all encompassing court which has the power to try all cases of gambling all over the world. Furthermore, gambling laws differ from one country to another. And if you set this kind of court, it will definitely need a huge manpower given that hundreds and hundreds of millions of gamblers are scattered all over the world.