How can I train my dog to obey me, in different types of places such as the park?
The problem is that your dog’s behavior has not been proofed in multiple places. Dogs aren’t good at generalizing. So he knows how to sit at home, but in a new place, outside, with other dogs or people around, all that training goes out the window. Look at this way: I teach you some math problem and then put you on a roller coaster and ask you to do that same math problem. You probably won’t be able to do it in the new exciting atmosphere. I proofed behavior by slowly upping the difficulty. If he can sit in the house, try it out on the front lawn. If he can sit there, try it in the park far away from other people and dogs. If he can do it there, try it closer to people and dogs. Try asking him for sits (or recalls or whatever) everywhere you can. You’re doing the right thing with teaching him by rewarding him with treats and tug, but you just need to start looking for increasingly more challenging places to ask for those behaviors. Right now you’re jumping from kindegarden to graduate