Figure 9.8 on page 194 refers to a method called defaultStore, but it is not described anywhere else in the book, nor is it described in the Xcode documentation except as a class method on NSUbiquitousKeyValueStore. Is this what you are referring to? If so, why is it relevant to the discussion of singletons on p.194?
I can see your confusion, as this is simply a typo between the second and third editions of this book.
In the second edition they used defaultStore, whereas in the third edition they have used sharedStore, so the text in the diagram should be sharedStore.