How did Sai Baba prove to Cholkar that he was all-knowing? I'm interested in the specifics of that interaction.

Sai Baba demonstrated his omniscience to Cholkar in a very personal and undeniable manner. After Cholkar fulfilled his long-held vow, which involved abstaining from sugar, he was visiting with another devotee named Jog. As Chapter 15 recounts, Baba, who did not even drink tea himself, instructed Jog to serve Cholkar "cups of tea, well-filled with sugar." This specific command was deeply meaningful because it directly referenced the secret penance Cholkar had undertaken. This act served as irrefutable proof that Baba knew the state of Cholkar's mind when he made the vow and was aware of the long delay, confirming his all-knowing nature and impressing the "stamp of devotion" on Cholkar.