In 2007, six-year-old Jazz Jennings went on national television to tell Barbara Walters the same thing she’d been telling her parents, siblings and anyone else who would listen: She was, despite her birth certificate’s insistence otherwise, a girl. Shy and sweet, Jennings answered Walters’ probing questions with the clarity and patience of someone used to explaining herself over and over again. “She was so charismatic, so charming and so clearly herself,” Laverne Cox says of first seeing that “20/20” interview. “Her humanity was so on display that you couldn’t deny she had the right to be who she was.” It...