"Dragon Ball Super" just introduced Kid Buu's reincarnate and seems like the character will have his own arc. Uub has been seen fighting with Goku in a World Martial Arts championship at the end of "Dragon Ball Z".
In the search for Android 17 last episode, Goku went to Dende to get help finding the long-lost Android. The Namekian happily helped Goku find the android, and he also steered Goku on the island where Android 17 is working as a ranger. But while on the way, Dende talked about a child that possesses martial art prowess, telling Goku that he is Kid Buu's incarnate.
Just like any other "Dragon Ball Super" arc, new characters and villains are introduced. It is possible that Uub will have his own arc along with a new threat to Earth's safety. according to Blasting News. The last time Uub was seen is as his Teen self on "Dragon Ball GT", in which he permanently fused with Good Buu making a being called Majuub.
The meeting of Goku and Uub has was on "Dragon Ball Z" end, where Goku and Uub fought in the World Martial Arts Tournament. Uub came from a poor home, and he uses his natural power to help feed his family, Comic Book has learned. He was seen as a little boy with dark a dark skin and has a mohawk hairstyle.
Though it is unlikely that Goku will meet Uub anytime soon in "Dragon Ball Super". Their meeting was set on the timeline after the Universe Survival arc and the arc seems to take its time. However, he can be considered as the Earth's most powerful warrior, surpassing Kuririn when the right time comes. In the meantime, fans should enjoy the comeback of their favorite "Z" characters as well as new characters this coming "Tournament of Power".