If you look at the Book of Fables entries under Extras before you start playing the episode, you will see a number of blank tiles with the number 3 in them. As you unlock the entries, the blank tiles with the number 3 will be replaced with an image corresponding to the entry. If you unlock all these entries, you will get the achievement for unlocking all episode 3 Book of Fables entries. The achievement will unlock even if you have unopened tiles for episodes 1 and/or 2. You can check your progression at any point while playing the game by pressing pause and opening up the Book of Fables.
Most of the Book of Fables entries are unlocked during normal story progression. There are three places where you can miss Book of Fables entries.
Spoiler free guide.
First missable Book of Fables entry opportunity:
When you first encounter Snow, say nothing. Instead, move to your left and investigate all items on a table. You will unlock a Book of Fables entry.
Second missable Book of Fables entry opportunity:
At the end of chapter 3, you are given three choices. Each of the three choices unlocks a Book of Fables entry. Depending on your first choice, you will go to either two or all three of the locations. Nevertheless, the circumstances differ depending on the sequence. From the standpoint of completing the episode, all three choices are acceptable. However, to unlock all three entries in a single playthrough, you must choose the second selection first, then go the location corresponding to the first choice, finally go to the location corresponding to the third choice.
First, choose the second choice when initially provided with the three choices. You will get to the location in time to uncover all information. When you get there, turn to your left and examine a statuette. This will unlock a Book of Fables entry for a character. Natural story progression will lead you to two choices. Choose the choice that corresponds to the first of the three original choices. Some people have stated that Book of Fables entry did not unlock so make sure you are positive in all your responses and offer employment. Finally, when you go to the location that corresponds to the third of the original three choices, this will unlock a Book of Fables entry for a location.
If you do not get all three missable entries, when you finish the episode, replay (rewind) chapter 3. The game will prompt you for a save file. You can either overwrite your current save file, overwrite an existing save file other than the current one, or create a new save file. Play through the chapter as you did before. When you get to the three choices, choose the selection corresponding to the entry you missed most likely the first selection.
This same logic applies if you opted to take a different approach from the one laid out above. Replay chapter 3 (note the save options mentioned above) and, when presented with three choices, choose the selection that did not unlock a Book of Fables entry on your first playthrough.
Third missable Book of Fables entry opportunity:
When you are given a choice between destroying an item or leaving it intact, each selection unlocks a Book of Fables entry. The two choices are mutually exclusive. When you finish the episode, replay this chapter (chapter 5) and make the opposite choice from what you made before. See the discussion above for further info on replaying (or rewinding) a chapter.
When you unlock the last Book of Fables entry, you will unlock the achievement for unlocking all Episode 3 Book of Fables entries.
Note: Once you load up a save file, the game will track the choices you make with that save file. So, make sure that you have the choices you want in a complete episode 3 playthrough save file. If you choose to replay a chapter and create a new save file and quit before the end of the episode; the resulting save is not a complete episode save file. If you select your current complete game save file and replay a chapter making a different choice; the game will now track the latest choice you made. Make sure you manage your choices the way you want them to occur for episode 4. You can always change the choices the game tracks by replaying a chapter with the choice you want to change and selecting your complete episode file as the save location.
Here is some additional info with spoilers: