My Mum sold my dog 5 years 이전 when i was 7 and i just found out as a 12 년 old. How can i get the dog back???

If your mother was the official owner, and I suppose she was because 당신 were seven and not an adult, and she sold it with all the paper there is nothing 당신 can do against it per law. 당신 could only ask the owner if he would sell it back but after 5 years I doubt so.
Sorry 당신 can't do anything because it was the dog of your mother, so it was her decision and 당신 weren't old enough to decide for yourself if 당신 were the official owner, but I doubt that too because 당신 were and are to young to buy a dog on the paper

Hi aleks, i am going to be honest with you, but after not having the dog for that long 당신 can't get it back unless the 초 owner gives it away. So if ur parent gave all the papers to the 초 owner, 당신 can't unless 당신 contact the AKC 또는 ask someone. But i'm sorry but 당신 can't get the dog back unless there's a reason tbh. And i actually do agree 당신 might have been to young for the dog and she didn't want 당신 to own it yet cause u were 7. My 프렌즈 in real life actually had something similar to ur problem were his mum said hes going to summer camp, 3 years later we have kept him since.So we could give him back but hes a good boy so we always send pics of him. Again i'm really sorry for not being able to get him.