Without knowing which works of literature you have read, it's difficult to build a strategic answer to that part of your question. I'll provide some ideas which I think speak to this prompt to help you think about the literature you have read.
Your thesis is basically written for you within the prompt itself. It should probably read something like this: Because of their unifying themes, ___, ___, and ___ prove to be works which speak to people regardless of life experience, and act as a mirror for readers's own life experiences.
Each body paragraph would then examine the three works you have chosen to include in your thesis, examining how each one uses themes, characters, and conflict to create a shared experience.
For example, I might choose To Kill a Mockingbird as an example. How do I then use this text to identify unifying themes? Although the novel is set close to one hundred years ago now, the conflict in the novel presents challenges that Americans still face today. Do we ever encounter a situation when someone is judged unfairly because of race? Absolutely. Have I ever encountered a Bob Ewell? You bet. I could also examine Atticus Finch, who represents a desire for people to be treated fairly and without prejudice, teaching his own children about the values of empathy and decency. I hope I can see little pieces of myself in Atticus, and I could certainly use some of his quotes in this paragraph to build a case for conversations I could have with others, such has this one: “You never really understand a person until you consider things from his point of view … until you climb into his skin and walk around in it.” Or this one: “You just hold your head high and keep those fists down. No matter what anybody says to you, don’t you let ‘em get your goat. Try fighting with your head for a change.” These are views that speak to people regardless of age, life experience, or personal circumstances.
These are the types of things you can begin to examine as you reflect upon the literature you have studied this year. Which ones generate an inner dialogue within you about a shared experience of all humans? Did you find any characters particularly representative of the positive or negative experiences you find in society? Did any quotes really stand out to you as great conversation-starters for engaging with others and transforming the ways we interact with each other? These are great questions to help you evaluate the literature and determine your areas of focus.
I hope this has helps! This is a powerful prompt, and I hope you find the literature that most speaks to you as you engage in this meaningful reflection.