You can see average video-view duration metrics in the:

A) Google Analytics
B) the “Audience retention” tab in YouTube Analytics
C) reports in AdWords
D) the “Campaigns” tab in AdWords

The correct answer is:

B) the “Audience retention” tab in YouTube Analytics

Explanation: You can use the Audience retention report to get an overall measure of how well your video keeps its audience. Use the report to see:

  • Average view duration for all videos on your channel
  • Top videos or channels listed by watch time
  • Audience retention data for a specific video for different timeframes
  • Relative audience retention for a video compared to the YouTube average for similar videos

Read more here: https://support.google.com/youtube/answer/1715160