There are 13 Optional Conversations found in The Last of Us: Left Behind. Although there are six chapters featured in this DLC, all of these Optional Conversations are found in 2nd and 4th chapter of the game.
The Last of Us: Left Behind Optional Conversations Locations
Like I have stated in my Artifacts Guide, these collectibles do not serve any purpose other than the sake of 100% game completion, and a Trophy tied to collecting these.
Optional Conversation #1
Location: When you see Riley coming out of trash, immediately look on the wall on your left.
Optional Conversation #2
Location: Near the very end of the first pair of escalators, turn to your right and keep on following the wall for this Conversation.
Optional Conversation #3
Location: Head back from where you turned right for the previous Optional Conversation and head straight. Try to walk along the benches on your left and you will come across a blue poster.
Optional Conversation #4
Location: Get all the way down to the bottom of second escalator and you will get it.
Optional Conversation #5
Location: For this Optional Conversation, you need to head inside the yellow tent and stand near the table.
Optional Conversation #6
Location: After receiving the previous collectible, come out of the yellow tent and keep on walking straight to get to the horse saddle.
Optional Conversation #7
Location: You need to head to the North-East corner of the area to get to the jar of eyeballs.
Optional Conversation #8
Location: For this Optional Conversation, all you need to do is wait for Riley to put on a new mask.
Optional Conversation #9
Location: Simply change your mask to Green Witch one and speak to Riley.
Optional Conversation #10
Location: You will come across a skull in the farther left corner of your screen. You will be prompted to hit Triangle about 8 times before the Optional Conversation.
Optional Conversation #11
Location: Just as the chapter begins, head straight and seat on the Merry Go Round Horse.
Optional Conversation #12
Location: After receiving the Pun Book, you need to press Triangle about 22 times before the Optional Conversation.
Optional Conversation #13
Location: The last Optional Conversation can be triggered by entering the phone booth.
Found anything missing or confusing, let us know in the comments below!