Do you know why the buddies in Battle of the Buddies (Example 5.1) are named "Norm" and "Cliff"? [You either know this reference or not, it's not something you can figure out on your own.]
This is neither easy nor obvious. Don't worry about exactly matching the three axioms referred to in the book. Just take what you've figured out about Shapley values so far from your reading to identify some properties about the Shapley value that you think are essential. It may help to compare this situation to that in Section 5.3, of the arbitration procedure Psi and Nash's axioms.