User blog comment:Silva92/Killua's Nen/@comment-4783583-20130726201501

as far as we know silva and illumi had killua's live completely planned out for him. Also the ones to get the requestsm are silva, zeno and maha and possible illumi. They probably only assigned targets to killua that didn't require any nen knowledge nor involve it. They would have thought it him when he was older. Also I agree kalluto learned it from the phantom troupe and milluki doesn't know it.