Sentence:  "Milly, it's true," she said, to be exact, "has no natural sense of social values, doesn't in the least understand our differences or know <WSD>who's who</WSD> or what's what." 
Meaning of the word marked with <WSD> tags:  The identities of specific people, understood in terms of such distinguishing characteristics as their backgrounds, prominence, achievements, jobs, etc., as a basis for comparing them and especially as a basis for ranking them within a social group.