Either 50% or 100% naked neck chicks, depending on if the turken is not pure or pure for the naked neck gene.
You often can tell if a bird is pure or not by the size of "bowtie"(patch of feathers on neck). Pure birds have either totally bare or just a small bowtie with few feathers, so the neck is very bare looking. Not pure have a much larger bowtie with many feathers covering most of the neck.
By the way, for the naked neck it does not matter which parent has it, can be turken rooster or turken hen crossed with other chickens and there will be babies with naked necks.