Question: how does majin buu know kamehameha?
Answer: This technique was first used by Majin Buu in his fight with Super Saiyan 3 Goku. After watching Goku use his Super Kamehameha, Buu decided to imitate it and fired the Majin Kamehameha at Goku, who deflected it back towards him. ... This attack was also used in Dragon Ball Super during Buu's fight with Basil.