Hi djtoze, and welcome to cruise-chat.
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.
Why NCL does not publicize this, I do not know.