It’s been awhile since I’ve played the game, but I’m fairly certain it explains that you have to target lock whomever you’re looking at. Eagle vision only shows characters that are doing things that can be added to the Encyclopedia, which is a more productive than arbitrarily trying to view every character you run into.

The character you are watching doing an activity will highlight then a log book update will show at the top of the screen once you are finished observing.
So far eagle vision has not helped me complete this.

It was very frustrating when I began working towards this and I spent far too long trying to figure it out. Glad it helped you. 😀

No problem. I get frustrated easily at silly things like this, so figured I’d help out the other rageoholics. 😛

It’s an optional side-quest that grants you an achievement upon completion. It’s for all the achievement whores out there as it has very little to do with the story. 😛

Obviously. Just assumed everyone understood that’s how you get the entries so didn’t feel the need to mention it. Thanks though!