I have seen this question twice over the weekend in the Facebook Group and figured I would answer here, as this is the kind of issue that can suck your time faster than a Hoover over a pile of dog fur.
First place to look is your WordPress Discussion settings. Are you allowing people to comment?
Next, let’s look at your Divi Theme Options. If you toggle over to Layouts, you can enable or disable comments on posts. This is the same place you enable Thumbnail images, which again can drive you crazy if you don’t know where to find that. As long as you are here, if you for some reason want comments on pages, then click on the Single Page Layout Tab and enable comments.
Still want more control over comments appearing on individual posts? Let’s navigate to a Post. If you look at the top right hand side of your screen you will see Screen Options, click this and you will get a menu of options. Toggle Comments on or off here with the check box.
As with most things involving WordPress or the Divi theme there are typically a few different places to hunt for the source of the issue and the same applies to the potential solutions for those problems.
If you are having any trouble after trying each of these then please let us know and we can see if we can help with a solution.