When a post is shared on the newsfeed, a stat, in the footer of the post, shows how many users have seen the post.
A user is considered to have seen the post if he has reacted (commented, liked...) or if the post post was in the viewport during several seconds.
Nb: it cannot be guaranteed that the user has read the post
A clic on the number of views displays a popup with the list of users who have seen the post.
The administrator can disable the possibility to know who has seen the post.