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

If your mother was the official owner, and I suppose she was because あなた were seven and not an adult, and she sold it with all the paper there is nothing あなた can do against it per law. あなた could only ask the owner if he would sell it back but after 5 years I doubt so.
Sorry あなた can't do anything because it was the dog of your mother, so it was her decision and あなた weren't old enough to decide for yourself if あなた were the official owner, but I doubt that too because あなた 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 あなた can't get it back unless the 秒 owner gives it away. So if ur parent gave all the papers to the 秒 owner, あなた can't unless あなた contact the AKC または ask someone. But i'm sorry but あなた can't get the dog back unless there's a reason tbh. And i actually do agree あなた might have been to young for the dog and she didn't want あなた to own it yet cause u were 7. My フレンズ in real life actually had something similar to ur problem were his mum 発言しました 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.