This chapter of the guide to Dragon Ball Z: Kakarot has a walkthrough for Good Ol' Goku side quest.
Time frame: From Majin Buu Reborn - Episode 8: Finale to No time limit
Reward: 238,977 EXP, 3x D Medal, Golden Compass
Where to start: West Forest Area, as Goku
To start this mission, you must go to the Sacred Land of Korin. There you will find Bora and Upa - they will give you a new substory.
The first part of your task is to talk to several people - all of them are marked on the map.
After collecting information, start looking for the item. The item is marked on the map. It is also marked in the game world - you shouldn't have problems with finding it.
Pick it up to complete the quest.