How can I show the product description on frequently bought together items?

In Frequently Bought Together you can show or hide the the product description visibility to better match the layout of your theme. 

For instance, if the widget is placed in a narrow column, it would improve the readability of the content if you keep the descriptions hidden. 

In the screenshot below, you can see the Frequently Bought Together widget below the add-to-cart button.

On the other hand, it makes more sense to show the product description when the widget is displayed full-width below the product section.

In the screenshot below you can see the Frequently Bought Together recommendation widget at the bottom of the product page when the descriptions are visible.

You can change the visibility very easily from the app preferences page in the Visual preferences section, just select the 'Description' icon in the visual selector, on the left, and check or un-check the 'Show the product description' option to meet your needs: