Xcode Preview Resume Button Shortcut
⌘ command + option + P is what you're looking for.
Quick Answer
Editor -> Previews -> Refresh
Refresh canvas shortcut
⌥ option + ⌘ command + P
Open canvas shortcut
⌥ option + ⌘ command + ↩ return
ð¡ Automated way to refresh the preview
Note that there is an option called Automatically Refresh Canvas that is enabled by default and helps you to not refreshing it manually again and again.
ð How to find ANY macOS apps shortcuts
In almost all macOS apps, you can use help menu to find the submenu item you want (some kind of preview in this case). And it will show you the exact location of the submenu alongside the associated shortcut:
I have searched for preview for this case :)