This is a topic of much debate. Basically, males do not have a G-spot in the same sense that women do. Although we don't have an equivalent G-spot, there are two areas that are extra-sensitive and can create deep pleasure, that are often called the male G-spot. Which one you consider a G-spot is up to you. They are:
1 - The prostate gland. The prostate gland can feel quite good when rubbed or stimulated, especially during orgasm, which can make the orgasm more powerful, longer lasting, and increase the ejaculation volume. To reach the prostate, you need to insert a well lubricated finger all the way into the rectum, and press toward the front of the body. The prostate gland can be felt through the rectum, and it feels like a walnut sized gland.
2 - The frenulum. The frenulum is located on the underside of the penis, just below the head and pee hole (urethra). In uncut guys, the frenulum is like a web of skin that connects the foreskin to the bottom of the head. Circumcision removed some or all of the frenulum, although many cut guys have a piece of it left behind that is still very pleasurable. I'm cut and have a piece of frenulum on the underside of my penis, and it is incredibly sensitice and pleasurable.
In my opinion, the G-spot to me is the frenulum, because its so incredibly sensitive and pleasurable. There is no other area of my entire body that is as pleasurable or as sensitive as this one tiny spot. The only thing that comes close is the head of my penis, and that's a distant second. The prostate, although it feels good to be stimulated, is not that incredible to me. Maybe it is more sensitive in some guys, but to me its no big deal.
So my vote for the male G-spot is the frenulum. Although from what I hear, its not as good as what women experience with their G-spot.