Summoning Shenron in Dragon Ball Z Kakarot can be done once you’ve collected all of the Dragon Balls in the game. As you collect these items you will see the Dragon Ball icons fill up on the top right hand side of the screen next to your mini-map. Once you’ve got all seven of the Dragon Balls collected you will be given the ability Summon Shenron.
To Summon Shenron you’ll actually need to go into the main menu and then head into the Dragon Balls option. You’ll then need to Set a Wish from the Wish List on the right hand side of the menu. Then you can scroll down to the Summon Shenron option.
After this a short animation will play and Shenron will appear to tell you he will grant you a wish. At this point your wish will be granted.
There are a number of different wishes that you can choose from. These include facing bosses again, getting a lot of Z Orbs, or getting a lot of Zenni.