This is a difficult question to give a balanced answer to precisely because there is still debate about the g spot. Your family doctor might give you one answer, a g spot sex activist would give you another answer, and a medical researcher who has studied female sexual anatomy would give you a third answer.
Because no one really agrees on what g spot means, arguing its existence becomes futile since the skeptic may be using different definitions and criteria. There are several studies published in established and respected peer-reviewed journals that are relevant to the question about whether the g spot exists.
The g spot was named for the German physician Ernst Grafenberg who first described "an erotic zone located on the anterior wall of the vagina along the course of the urethra that would swell during sexual stimulation."
This is a common question both for those who have a g spot, and those who want to learn to stimulate them. One of the problems people have when trying to locate the g spot is that they are expecting it to be a magic button, which, once pressed, immediately delivers mind altering sexual pleasure. Sadly this only happens in old Woody Allen movies.
There are hundreds of sex toys designed and marketed as g spot vibrators or g spot dildos. Most sex toys that are safe for penetration, and firm enough that they wont bend when inserted into the vagina, can be used for g spot stimulation. Whenever a sex toy is hyped, like a toy designed to stimulate the g spot, people might imagine something akin to a heat seeking missile that will search and satisfy on its own.