Take pictures of them.  You won’t be able to complete this puzzle until you’ve visited The Dining Room. 

Can you match the pictures you took back in the kitchen with toxicology report in the Dining Room?

Matching the toxicology report to the drink ingredients from the kitchen tells you that the two drinks consumed in the dining room were a Negroni and a Triple Crown.  Those are the drinks that Plum and Scarlett were drinking.