This achievement is for finding the last (24th) journal entry, which is not one of Sam's 23 entries.
I suppose all 3 other solutions are right, they just weren't what I was looking for when I came here, meaning that I was in my first playthrough, not speed-running, just enjoynig the game, and found myself missing just a few journal entries, and those speedrun videos are just rushing through everything and I just wanted help with this particular achievement, not the entire speedrun.
So, if you're in the same situation I was in, you'll have every room unlocked already. All you have to do is go to the garage and look for a blue recycle bin on the far end, open it, and grab a can. Then, go to the garage doorway and look up to the ceiling, you will see a purple ball on one of the beams. Throw the can at it, and the ball will fall to the floor. Grab the ball and take it to Sam's room. Drop it inside the room and close the door, which has a net on it. Grab the ball, approach the net and you'll see a text that says Dunk!. Dunk the ball and the achievement will unlock. Also, watch the TV haha
I found this video on YouTube, all credit to YouTube user/uploader Respawn Studios. It shows how to get the achievement.