Put the dragon on the palm of your hand, tail pointing at your nose.
Lift the tail straight up so you can see the underside where it joins to the body.
You will see not an organ, but one or two bumps under the skin. If you see two parallel bumps, forming the shape of a vertical slot, you have a male. One bump horizontally is a female. Weird, but here's why:
You are looking at either the one set of ovaries, horizontally installed, or TWO penises, left and right, vertical and parallel. Go figure. Now remember, breeding is not heavenly magic, you need at least one of each of these to breed. It's how life works, until Monsanto gets to patent all the genes on earth.
