You want to see how many (and maybe which) records have been sent a specific piece of content by a nurture stream
In the Streams tab of your engagement program, change your view from "Content" to "People". You will see numbers below each piece of content indicating how many were last cast this piece of content and how many have been cast it total. Click on one of these numbers to see the specific records which constitute that total.
Please note that the last cast is not necessarily the most recent cast of the Engagement Program, it is the last time that piece of content was sent by a cast. The "Last Cast" of the first piece of content may be from three weeks ago, while the last cast of the third piece of content may be from this week.