In a user's Profile page, you can see which card Details views that user has viewed most recently or most frequently. You do this in the Viewing tab, which is located in the tab row under the user statistics panel.
To see what cards a user has been viewing,
Navigate to that user's Profile page by clicking that user's profile picture anywhere it appears. If you want to see your own cards, you can access your personal Profile page by clicking your profile picture in the top right corner of the screen. (If you have not yet selected a profile picture, a icon appears instead.)
Click Viewing in the tab row under the user statistics panel.
In this tab, you can toggle between Recently Viewed and Most Viewed. Cards the user has viewed most frequently/recently appear higher in the tab, and cards he/she has not viewed as recently/appear lower in the tab. If you click a card, its Details view opens.