Guix calls "reverse dependencies" "dependents".  You can list them with:

--8<---------------cut here---------------start------------->8---
> guix refresh --list-dependent webkitgtk
Building the following 2 packages would ensure 3 dependent packages are rebuilt: eolie@0.9.45 gnome@3.24.3
--8<---------------cut here---------------end--------------->8---

Hope that helps!

-- 
Pierre Neidhardt
https://ambrevar.xyz/