Lead Developer
Have you tried adding the CSS from the first page of this topic?: https://generatepress.com/forums/topic/caption-below-image/#post-4011
Since you’re using Exhibit as your child theme, you’ll want to add it using a plugin (#2 and #3): https://generatepress.com/knowledgebase/adding-css/
Documentation: http://docs.generatepress.com/
Adding CSS: http://docs.generatepress.com/article/adding-css/
Ongoing Development: https://generatepress.com/ongoing-development