When it comes to synonyms for the phrase "hath someone pegged," there are a few options to choose from. One such synonym is "understands," as in "She really understands him well." Another option is "knows," as in "He knows her inside and out." A more casual synonym might be "gets," as in "He really gets me." Additionally, one could use the phrase "has someone figured out," as in "She's got him figured out." No matter which synonym is chosen, the meaning remains the same: the person in question has a deep understanding or insight into the other person.