Can you tell me the story of how Sai Baba fulfilled the unspoken wish for khaja for his devotees, including Laxmichand?

Certainly. The story from Chapter 28 recounts how a devotee named Lalaji developed a craving for khaja (a sweet) after having it once as prasad. The next day, when devotees were wondering what food offering to bring, Sai Baba specifically ordered them to bring a plate full of khaja, thus fulfilling Lalaji's unspoken wish. At the same time, another devotee named Laxmichand was suffering from intense hunger and back pain. Demonstrating his omniscience, Baba said, "Hunger has come, that's good. There should be medicine for back pain. Now the wind of khaja has blown." As Chapter 28 explains, this act of knowing Laxmichand's inner state and fulfilling the collective desire for khaja filled the devotees with wonder and joy, solidifying their faith.