I have a Nikon F3 and an AF-S Nikkor 50mm 1:1.8 G Lens. What aperture control Enabler do I need?
Assuming you're talking about mounting the lens to the camera in the normal way, then in order to control the aperture on a Nikkor "G" lens, you need a compatible camera body. The F3 is not compatible with Nikkor "G" lenses, it that it has no way to control the aperture.
If you're talking about reverse-mounting your lens to your camera body for macro work, then you can control the aperture of any Nikon F-mount G or D lens by using a variety of options. See this question for more information: Is there a way to adjust the aperture of a Nikon lens without a camera or physical aperture ring?