This chapter of the guide to Dragon Ball Z: Kakarot has a walkthrough for Not Too Quick on the Uptake side quest.
Time frame: From Android Terror Arrives - Episode 8: Fleeting Normality to Episode 9: Gohan Unleashed
Reward: 116,001 EXP, D Medal, Ultra Brain Bread
Where to start: Western Forest Area, as Goku.
To start this mission, you must go to the Sacred Land of Korin. There you will find a team that will give you a substory.
Your task is to fly to a specific area and collect the item. It is located under the rock, just behind the huge tree.
Go back to the quest giver and receive your reward. Despite the fact that the mission seems to be officially completed, you will have to fight another battle. Once you are done with it, you can go back to exploring the world.