How did Sherlock Holmes know was working as a doctor again?

Sherlock Holmes deduced that John Watson was working as a doctor again by observing subtle clues, such as the presence of medical books and instruments in Watson's home, as well as the smell of antiseptic. Additionally, Watson's demeanor and the way he recounted his experiences hinted at his return to the medical profession. Holmes's keen powers of observation and deduction allowed him to piece together these details effortlessly.