President Kennedy's assassination
President Kennedy's assassination is symbolic of lost potential. After speaking with his friend Al Templeton, Jake comes to sincerely believe that if he travels back in time to 1963, he will be able to prevent President Kennedy's assassination. Like Al, he believes that the world would have been a much better place had Kennedy not been assassinated. Most significantly, they believe that the Vietnam War would not have occurred, saving the lives of millions of Americans and Vietnamese. Because Kennedy died, the world became worse off under the tutelage of President Johnson. And they want to rectify that.
Al's diner
Al's Diner is a symbol of the past. Diners, which have traditionally been thought of as old-timey places in literature, are places where people get together, talk, and discuss the past. It is no wonder that Al's diner is instrumental in Jake's mission to the past. At the diner, Jake learns more about the period he is traveling back to, about his mission, and about the time portal he will use to travel back.
The library
The library where Lee Harvey Oswald plans to shoot President Kennedy is a symbol of the depravity of man and an opportunity for Jake. Only a depraved individual would take the life of another innocent, helpless person. In real life, Oswald did just that when he shot President Kennedy, showing his true nature. For Jake, though, the library represents an opportunity. If he is able to intercept Oswald, he will be able to enact his plan and stop the assassination, which he ultimately does.
The grassy knoll
For Jake, the grassy knoll is symbolic of unanswered questions. Before he travels to 1963, Jake considers the possibility of other shooters. For instance, Jake questions if he will discover that the "grassy knoll" conspiracy theory is true (that is if there was another shooter on a grassy knoll who worked with Oswald to kill Kennedy). Although Jake goes into his journey better prepared than most, he still has things that trouble him.
Jake getting distracted
Jake getting distracted by things he doesn't expect is a common motif in 11/22/63. On several occasions, Jake gets distracted by things and people around him. Perhaps most significantly, he gets distracted by a beautiful woman named Sadie, who captures his attention and causes him to lose track of his mission.
