Where is the oil plug on a 1992 harley Davidson dyna super glide?

There is no such bike. In '92 there was an FXR Super Glide, an FXDC Dyna Glide Custom, or an FXDB Dyna Daytona.

Do you mean oil drain plug? If the bike is, indeed a Dyna, there's a plug on the bottom of the oil tank which is below the transmission. If it's an FXR the drain hose for the oil tank is under the left side plastic cover.