How to check if a View was cached? Is there a simple way to check (example: see from UI or browser developer tools) if a rendered View was retrieved from cache or just generated on the page load?

This would need to work for every view display, like a View Content pane embedded in a Panels page.

Would this need custom code or is there a module or any-other-simple-way for this?

Thanks
Caching only works for anonymous users (people who are not logged in). 

So, a simple test would be to add new content to your view or make a change to your view. Ex: change your view title. 

On another browser have your page open, but as anonymous. If your view doesn't change, it means the cache worked. 

The View will NOT change to anonymous users until you clear the cache.