Don't have an account?
Search for an answer or ask a question of the zone or Customer Support.
You need to sign in to do that
Sign in to start searching questions
Signup for a Developer Edition
Sign in to start a discussion
If you can able to find the info , please post on this thread ..
Seen-by information is not available in any reports.
https://releasenotes.docs.salesforce.com/en-us/summer17/release-notes/rn_collab_seenby.htm