This chapter of the guide to Dragon Ball Z: Kakarot has a walkthrough for The Parent Trap side quest.
Time frame: From Majin Buu Reborn - Episode 8: Finale to No time limit
Reward: 327,955 EXP, D Medal, Super Brain Bread
Where to start: West Area, as Vegeta.
To start this mission, you need to talk to your son. He prepared an unpleasant surprise for you.
Your task is to go to the specified point and fight Gotenks. This enemy can be several levels above yours. However, you will fight alongside a partner.