Looks like just from a photo that the old axle is a bolted type and all the replacement ones mentioned have been QR hollow axles. I'm sure that the hub could be converted if the owner wants that, You'd need a skewer too then.

A caliper, or even a ruler is your friend. Guessing is just guessing.

If your guy brought the old axle into an LBS they can find a suitable replacement in a snap. Then it is either have them install it into the hub, or he can bring it back to you. Most likely there will need to be some fine-tuning of spacers/washers to get back to the original OLD to match the fork.