In order to display the image caption, you will need to customize the Image module or use a special plugin, which is much easier.
Follow the steps below to enable Image Caption under the Divi Image module:
Install and activate the Free Divi Image Helper Plugin
Add the caption text to the image in the WordPress Media Library:
Navigate to the WordPress Dashboard / Library.
Select the image that you want to add a caption.
Look for the Caption field and add some text.
Now add the Divi Image module to your Divi Builder Layout.
Look for the Enable Image Caption option under the Elements toggle:
