Hey @Matan Zrihen Racheal from the support engineer team here 

It looks like you worked this out with my teammate already but for future viewers, there is not a default report that includes the percentage of conversations that have completed a CSAT. You would need to do some math here and find the number of closed conversations vs the number of ratings. Something else to keep in mind, not all conversations are eligible for a CSAT rating (more on that here). I can see how having a more straight forward way to pull up on this data would be beneficial so I will definitely flag this as a feature request for the team to consider!