You should use Unique Reach and Frequency to measure how many people were served your ads and how many times they were each served across devices and formats in addition to fundamental video metrics such as “Video played to”.

• Brand Lift
• Viewability with Active View
• Unique Reach and Frequency
• Reach Planner

The correct answer is: Unique Reach and Frequency

Explanation: To measure reach and frequency in a Google Video campaign with an awareness goal, use unique reach and frequency metrics such as Unique Users, Average Impression Frequency per User, Frequency Distribution 1+, 2+, 3+, 4+, 5+, 10+. These metrics provide insight on how many people were served your ads and how many times they were each served across devices and formats, going beyond basic cookie measurements. These metrics can be viewed by adding columns for these metrics to the statistics table and selecting a specific time period in the dropdown menu.

Read more here: https://support.google.com/google-ads/answer/2472714