A strong place to start is Karsh: A Biography in Images by Karsh himself. Based on the community feedback, it does more than present the photographs: it also includes commentary on why particular portraits were made the way they were, including the intended effect of the pose, perspective, and lighting. That makes it especially useful if you want insight into the character and psychology behind his portraits rather than just technical setups.

If you’re hoping for step-by-step “how to light like Karsh” recipes, this may not go very deep technically. But for understanding his thinking and approach to portraiture, it sounds like the best starting point.

As a companion resource, karsh.org is also worth visiting for background information and anecdotes that add context to his work.