Note that system design interviews are often completely customized and adapt on the fly to the applicant's responses, so there's no way to do a "cracking the system design interview" the way you can with coding problems. When I give coding interviews I have one question that I give over and over again, learn the ins & outs of the questions and how candidates go wrong, and score based on whether the candidate can complete it, or how close they came to a valid solution if they couldn't. When I give system design interviews I pick a topic that's something that both the candidate & I have had experience with, start out with "How would you design X?", and see where the candidate goes, drawing on my background knowledge to prompt further about cases to consider and situations that might come up in the real-world implementation of the system. The candidate is generally driving the interview, because at the level where system design interviews become necessary, the candidate should know how to pro-actively anticipate problems.
