I have been to the local plumming supply dealers and they have been unsuccessful in providing me a solution. The pipe appears to be an exterior drain that connects to the kitchen sink. This was built as part of the original house when the house was built in 1983. The pipe is white and definitely PVC and threaded. I would like to find a threaded cap to close the drain. Any thoughts as to what type of pipe this is and where I can find a cap would be great.

Get a Fernco adapter that will slip over the threaded part. Find a plain cap, 2"? that will slip into the other end. You can reduce 1/4 " or more with these fittings. We use this system to block off non pressurized pipes. You may also be able to cement a PVC test plug into the pipe. They only cost 25 cents or so.

So there must be a glued on coupler on the end of the PVC pipe, is it male or female? pvc couplers - Google Search