John Gill Commentary 1 Samuel 17:56

"And the king said, Inquire thou whose son the stripling is." — 1 Samuel 17:56 (ASV)

And the king said, inquire you whose son the stripling [is] .
] Still the question is the same, being very desirous of knowing of what family he was, for the reason before given, (See Gill on 1 Samuel 17:55).