Your dog learns to sit if he wants attention.
Let your dog smell a treat in your hand, then just move both your hands towards your belly and wait… (have patience). Your dog will follow the treat with his eyes and after a moment will lower his bottom to the floor to be able to keep watching it. As soon as he does, say GOOD BOY and give him the treat.
Practice this a few times a day. Remember to say nothing! Your dog must think of what to do himself – and he will! He earns something tasty when he does.
Check after a few times if he knows what he must do when you put your hands on your belly. If he sits of his own accord, he knows what the gesture means. SAY PLEASE = SIT
If he knows how to earn a treat, he will come to you by himself and sit before you. Pleeeeeease can I have a treat? In the beginning that’s not a problem. He definitely knows how you want him to ask attention. With time, just say GOOD BOY giving him a treat only once in a while. Your dog has learned to sit before you if he wants attention. Not jumping up but sitting before you. If you would like to remind him, you just have to put your hands on your belly, and voilá!… your dog sits.