36 - After returning to the cabin from the elfess in an agitated state (when Tovenaar insistently wants to show some erotic pictures) and Lauren suddenly walks in, you need to stand silently (refuse to engage her) and she will leave. That's when you'll hear the knock on wood. That's when the scene happens.
As for 48 - it's a mystery to us why you don't have it, because it's a mandatory plot scene.
What version are you playing?