Here's a video guide that I made covering all the collectibles for this episode. I've also made some notes below describing where they are.
The Walking Dead: The Final Season Episode 2 Collectibles GuideThere are
three collectibles in Episode Two and they can be found in the
Greenhouse/Lab areas which is towards the
end of Act 2....
Boar Skull - Found directly behind you before going inside the Greenhouse.
Mushroom - Can be found inside the Greenhouse on the flowerbed that's directly in front of the cabinet where you get the Barbed Wire from.
Venus Flytrap - Can be found inside the Lab, it is directly in front of you
on the flowerbed on your left.
Once you have all three collectibles you can place them in the following locations in your sleeping quarters.
Boar Skull – Can be placed on the shelf on the right side of the room.
Mushroom – Can be placed directly underneath the Boar Skull.
Venus Flytrap – Can be placed on the bed side cabinet next to the bunk beds.
Hope this helped.