Cobie Smulders spent eight weeks training in various martial arts to prepare for her role in this film.
The shirt Jack Reacher wears in the first diner scene is the same shirt he wears throughout the first Jack Reacher (2012) movie.
The film is based on the eighteenth "Jack Reacher" series novel by source novelist Lee Child. "One Shot," the basis of the first film Jack Reacher (2012), is the ninth book, which means this movie is not necessarily a direct sequel in terms of the book series.
The opening scene of the diner in which Jack Reacher exposes a small town sheriff who is running a human trafficking ring was inspired by the novel "Worth Dying For", which preceded "Never Go Back" in the chronology of Reacher novels. In the novel, Reacher is passing through a small town in Nebraska when he stumbles upon a sex trafficking ring run by a prominent local family (not the police). After breaking it up, the small town folk ask Reacher where he's going next and he says that he's going to Virginia to see a woman named Susan, who he has only ever spoken with on the phone. 'Susan' is obviously Susan Turner (Cobie Smulders), an Army investigator working out of the DC area (in Virginia) and as seen in the opening minutes of the movie, his interactions with Susan take place over the phone. (Though in the novel "Worth Dying For", she had no involvement, nor did the government, in exposing the ring. That was created for the film.)
Lee Child: source novelist plays a TSA agent who is seemingly ambivalent to the fact that Jack (Tom Cruise) does not really match the stolen ID he is using to board the plane. This is a nod to Child's support of the "controversial" casting of the diminutive 5'7" tall Cruise as Child's 6'5 tall," 250lb weighing, and 50-inch wide-chested character of Jack Reacher. Despite a lot of fan backlash at the casting of Cruise, Lee responded: "Obviously, Cruise doesn't match the physical description of Reacher in the books, but the movie is not going to match the book anyway."