Can you give me an example from the Satcharitra of Sai Baba knowing a devotee's inner thoughts?

Yes, Chapter 28 provides a clear example of Sai Baba's omniscience through his interactions with the devotee Laxmichand. One night during the Chavadi procession, Laxmichand saw Baba coughing and privately thought to himself that it might be caused by someone's "evil eye." The very next morning in the masjid, Baba spoke to Madhavrao, but clearly for Laxmichand's benefit, saying, "Yesterday I had much coughing; is this the effect of an evil eye?" Baba repeated the exact thought that had been in Laxmichand's mind, causing the devotee to wonder how Baba could possibly know his private thoughts, confirming that Baba dwells in everyone's heart.