Below is the solution to the Cluedo puzzle.
What cards are accounted for at first glance?
Jeroen doesn't have P2 or W2
Rob doesn't have P4 or K8
at least one of P6 W6 K5
at least one of P4 W2 K7
at least one of P4 W6 K5
at least one of W2 K5
at least one of W4 K5
at least one of P6 W4
The question stipulates that if a person asks for a card the second time, you have to assume that they weren't shown it the first time. (as... I think it was Black here who shows that this isn't necessarily true - this is a dog-eat-dog group).
Jeroen asked K5 twice : first in round 3, when Rob showed. Assuming he didn't get to see K5 on that turn, he definitely didn't see P3 since Merel has that, so Rob would've shown W2.
In turn 7 Rob asks P4 W2 K7. He asks for P4 later, so assuming he didn't get to see that - we also assume he has W2. Jeroen would've shown K7.
In turn 6 Jeroen asked for P1 W4 K5. He asks again for W4 in turn 12, so didn't get to see it. P1 is owned by Jeroen. Rob would have shown K5.
In turn 1 Rob asks P6 W6 K5 - Rob asked for W6 later so Jeroen wouldn't have shown that. We now know Rob has K5 himself, so Jeroen would have shown him P6.
The killer must be P4.
In turn 13 Rob asks P4 W6 K5. Jeroen wouldn't have shown P4 since he doesn't have that, K5 is owned by Rob, so Jeroen would have shown W6.
In turn 12 Jeroen asks P6 W4 K4, Rob shows not P6 (owned by Jeroen) and not K4 (owned by Merel), but W4.
The murder weapon is W5.
At this point we know all the cards Jeroen has. There are 3 missing rooms, 2 6 and 8.
In turn 9 we learn Rob doesn't have K8.
K8 is the murder room.
All other non-Clue/Cluedo discussion.