The default appearance of the Single Post layout is shown below:
There are four distinct areas.
Post Content, which contains:
The post content (text)
Create a theme builder template assigned to all posts
Go to WordPress Dashboard → Divi → Theme Builder.
Create a new template by clicking on the
+icon and click on Build New Template.
Assing the new template to All Posts.
Click on the Create Template button.
Click on Add Custom Body and choose Build Custom Body.
Insert a new 1-column Row.
Insert the Post Title module - this will be used to display the Post related details:
The Post Title
The Post Meta information
The Post Featured Image
Insert the Post Content module - this will be used to display the actual content of each Post.
Insert the Comments module.
The starting layout should look like this:
Create the Author box
We will use the Person module and Divi's feature called Dynamic Content.
After the Post Content module and before the Comments module, insert the Person module.
Hover on the Name field and click on the Dynamic Content icon.
Choose the Post Author from the Dynamic Content List.
This will display the Author's name of each single post.
In the Name Format, choose how you would like to display the Author's name. A good option would be the First & Last Name option.
Enable the Link Name option and choose Author Archive Page.
For the Body, click the Dynamic Content icon and choose Author Bio.
This will display the Bio text, which is set for each Author in WordPress Dashboard → Users.
Expand the Image option group, remove the default placeholder and, using the Dynamic Content option, choose Author Profile Picture.
The final result: