The deck plans for N. Jewel do not show laundromats -- however, I have read in several reviews that they do exist. From what I can gather from these reviews and other searches, they are located opposite cabins 5072, 9088, and near cabins 10081 and 11062. This is where you will also find irons for passenger use.
There are laundry rooms on the Jewel, on four separate floors. I used the one on deck 10. It is located midships, across from room 10081. There were 3 washers, 3 dryers, 2 ironing boards. The washers & dryers do not cost. There is a dispenser for detergent which costs $1.00.
The Laundry Rooms on Decks 5,9,10 and 11 are on the inside portion of their respective passageways, slightly forward of the aft stairways. I learned that the door handles into the laundry area was differnt from the cabin door handles. (They were round)
and because of their difference,could be seen from some distance away.