He’s asking you to quantify how much it would take to make sure everyone has “enough”, and that the wealth in society currently exists to meet those conditions.
Keep in mind that your claim that there is “enough” has important implications beyond just mere stocks of grain. Merely claiming that there is “enough” sitting around says nothing about distribution, which, I believe, is what you’re getting at. But distribution is much more complex than just sending a boat over to the areas where there isn’t “enough”.