Under the US Copyright Act, you cannot copyright titles. That is because titles are too short to be protected. Copyright law protects original works fixed in a tangible medium of expression (e.g., your novel written and saved on Microsoft Word). However, when it comes to titles, they are considered "short phrases." They're too de minimis to be copyrightable. This is why you may see the same title for multiple books or films.
Although you cannot copyright a title, you may be able to trademark your title. However, there's a caveat. Single titles are generally not eligible for trademarks. Trademarks function as identifiers of goods and services, and consumers may have trouble identifying you as the author of the title, especially if there are many books that share your title. Think of it this way. If a bookstore carried your book and every other book with the same title on a shelf, could a consumer ID you as the author? Probably not.
Nevertheless, if your book becomes successful and you're able to claim "secondary meaning," meaning your title has earned a certain level of fame, you may be able to trademark your single title. In that same example, if your book has become a bestseller selling millions of copies, when consumers hear your title, they may automatically think of you. In that case, you may be able to trademark a single title.
What about your titles as part of a book series? You will have a much easier time trademarking because consumers may be able to associate you as the identifier of the book. The same goes for characters. For example, a famous character may become associated with a certain series, where readers may expect the author to have written a book that includes that character when they see it in bookstores. Think of Harry Potter. When you see Harry Potter, you think of JK Rowling and vise versa.
I hope this helps in determining whether to trademark your title.
Disclaimer: This article is for information purposes only. It is not be considered legal advice nor to be construed as such. If you have a legal issue, contact an attorney near you.