I roughly know the setup of an interview day for entry level consultants:
- math test (nothing really fancy, but some pricing calculated stuff)
- 3 interview rounds, almost definitely with a case in each one. Be ready to draw, calculate and reason the price/demand function. Did I say that SKP is quite specialized on Pricing? :-)
Best to read: Basic marketing / pricing literature, so that you have an idea what they want from you. Company website, so you know what they published recently.
Generally, as you will have noticed in the first interview, SKP people are down to earth, solid in their expertise and a friendly bunch. That is true for the Bonn office as well.
Hope this helps a bit. Best of luck to you!