GE dishwasher

Looks a lot like a kitchen sink drain stopper. How it got into the dishwasher is anybody's guess. The proof will be when it fits in the drain basket snugly.

Type your model number in a search engine with the word "parts". A list of appliance parts selling places will pop up.

Most will have an exploded view of your machine, along with a parts list.
Scroll the list's pictures to see if you find that mystery part. Next find it on the exploded view to know where it belongs on the machine.

Hope This Helps!
Paul