haven't got a spanner that'll grab it inside the freehub body
Once you have the driveside lock nut off, the one should only be finger tight. If you can't get a wrenching there, pliers should provide enough grip on the cone flats to allow you to spin the axle out.
I think there should be wrench flats on the NDS cone, it's possible that the dust shield has become dislodged and is obscuring them.
There's a washer① then a spacer② (both round) then the cone which has the dust shield③ pressed onto it. If you push the dust shield into the hub shell where it's supposed to be, you should see the flats on the cone
Once you have the driveside lock nut off, the one should only be finger tight. If you can't get a wrenching there, pliers should provide enough grip on the cone flats to allow you to spin the axle out.
I think there should be wrench flats on the NDS cone, it's possible that the dust shield has become dislodged and is obscuring them.