Which is a method for evaluating performance of engagement ads created with the Ad gallery?
Funnel visualization report
AdSense reports in Google Analytics
See instances where customers place their cursors over your display ad for a second or more. This can help highlight ads that may keep customers’ attention without an actual clickthrough to your website. This usually demonstrates an ad that needs a stronger call-to-action for the customer.
Read more here: https://support.google.com/adwords/answer/2456138?hl=en