Can you describe an instance where Shirdi Sai Baba demonstrated his omniscience to a devotee named Laxmichand?

Yes, Chapter 28 of the Shri Sai Satcharitra details an incident with a devotee named Laxmichand. Laxmichand had a private thought that Baba's cough might be the effect of an 'evil eye.' To his astonishment, when he went to the masjid, Baba spoke aloud, saying, 'Yesterday I had much coughing; is this the effect of an evil eye?' This revealed to Laxmichand that Baba knew his innermost thoughts, causing him to wonder if Baba dwells in everyone's heart. This experience solidified his devotion, and he pleaded for Baba's continued grace and protection before returning home.