The adjustable cone has wrench flats; the fixed cone does not. It's easy to tell the difference, if you can see the cones - they're awfully hard to get a good look at. Inside the fork, there's a locknut, then a fairly thick spacer, and then the cone. Probably, no more than a millimeter or two is showing - which makes it hard to spot those wrench flats. Try using a bright flashlight and see if that helps.

Edit: Please ignore the stuff in the silver text - it's completely wrong. I was thinking of the rear hub for some reason; the front hub has no locknuts other than the wheel mounting nuts on the outside of the fork. I woke up this morning and realized that I had typed something completely stupid, and it needed to be corrected.

But still - if you can get a good look at the cones, you ought to be able to see which one has the wrench flats, and a strong light might help. That part, at least, was right.