This drawing took a little more prep work than my usual picture research. I easily found a picture with a perfect expression of the character of John Reese (at left), but his clothing in the picture isn't typically what Reese wears in the show. Any Person of Interest fan knows that a true portrait of John Reese is of "The Man in a Suit." So I did some more digging and came across a very similar pose, only reversed, where he was wearing his usual white dress shirt, black suit and black jacket (at right). 

 

Some very quick Photoshop work later and I had the perfect picture to draw. Sure, it's not the prettiest Photoshop work, but it suits the purpose as a reference image!