There is only one axle nut. What part of the rear wheel are you referring too exactly? https://www.ebay.co.uk/itm/Ducati-M...958772&hash=item5445476cc3:g:4FQAAOSwWxNY2mqQ http://www.ctmoto.co.uk/
It's an rear wheel spindle with just a locking flange. Though I am prepared to be corrected. https://www.bike-parts-ducati.com/ Find your bike & click on items on images to be linked to part number & description'
To be fair i never even thought of checking the part numbers! *writes note to remember next time before asking