There is no such thing as reserving a title. The better question you should be asking is: "Does my title fit my book?" The other question you should be asking is: "Does my title attract my target audience?"
The simplest thing to do is to google the title (put the title in quotes).
Titles cannot be copyrighted, but sometimes titles can have elements that are trademarked. E.g., if you were to write a book titled, Harry Potter and the Silver Spoon, you'd be one mail-cycle away from receiving a cease-and-desist letter.
However, if you were to write a novel titled, The Tower Treasure, you'd likely have no problem, despite the fact that that title is the famous first-ever Hardy Boys mystery.
Caveat: I am not a lawyer, and I'm just presenting general facts as I understand them.
Sometimes even an author's name can be trademarked. If your real name were Ann Landers, you might not be able to use it if you were writing self-help books. These situations, however, would be rare.
Edit: I do google tentative titles that I'd want to use, just to make sure that, even if it duplicates another title, it would not create some sort of significant confusion among potential customers of either tome.
Edited by: Joseph M Erhardt on May 22, 2017 7:09 PM