Spoked rims need inner tubes, unless the spokes do not go through the rims but have a special setup like on the GSA, on Moto Guzzi's or like on the Super Ten. Or when there is an aftermarket system like Tubliss installed.

The fact that there's a nut means that it has an inner tube. Valve stems on tubeless rims have no need for the nut.

If it is leaking at the bottom of the valve stem, replace the inner tube.