This is actually veeeeery easy. A pokemon's amount needed to level up from empty is random. That said, it's just a random number suiting its level. Getting Experience, too, is easy. There are four ways to do so.
1. Battle and Win. Easy enough. When you battle, the amount of exp you'll get from that pokemon (again, random) is displayed under its name. Beat it and you get that amount. If more than one of your pokemon beat them, all without fainting, divide by how many pokemon you used (again, something I'll do)
2. Requests and Quests (yes they're different) Even easier...or it should be. When you accept a Request, you recieve a form. On the form is the amount of experience your pokemon get for completing it.
3. Training. This is the easiest one. Why? There's absolutely no chance of you getting hurt in return. You train against the environment or just train your pokemon to do cool things for battle. The catch is that you don't get a lot of experience from this.
4. Successfully Complete Appeals. This is probably the hardest one because it's based on how much the Admins/Mods admire your appeal. Basically, though, if you made it to the battle portion of the contest you're competing in, tah-dah, you get Exp.
All Easy yet all taken for granted...