Can you recount the story of the Yoga practitioner who had doubts about Sai Baba in Chapter 23?

Certainly. Chapter 23 narrates the story of a practitioner of Yoga who, despite having thoroughly studied the Yoga Shastras, could not achieve Samadhi. Hoping the 'King of Yogis' Sai Baba could help, he came for darshan with Nanasaheb Chandorkar. However, upon arrival, he saw Baba eating bread with onions and a strong doubt arose in his mind, thinking, 'How can this man remove my doubts?' As the chapter explains, Sai Maharaj, being omniscient, perceived this thought and said, 'Only those whose digestion is strong should eat onion.' This direct response to his unspoken doubt startled the Yogi, who then surrendered with true devotion, had his doubts resolved, and returned with a happy mind.