Here is the full list of all 18 Knock-knock achievements.
Chose to lock The Lodger inside the cabin and remain hidden
Turned into a doppelganger
Managed to hide succesfully ten times
Remembered the story of the Lost Child
Found five diary pages
Chose to go into the woods
Found a diary page
Entered ten haunters
Touched the weeping one
Saw all fragments of reality
Managed to hide succesfully five times
Entered a haunter
Turned the light on in every room
Managed to hide succesfully
Entered a breach
Saw three fragments of reality
Turned the light on in a room before a breach opened
Saw a fragment of reality