Albert Barnes Commentary Job 2:5

"But put forth thy hand now, and touch his bone and his flesh, and he will renounce thee to thy face." — Job 2:5 (ASV)

But put forth thine hand now— Satan felt that he had no power to afflict Job without permission. Malignant as he was, he knew that God only could subject the holy man to this trial—another proof that Satan is under the control of the Almighty, and acts only as he is “permitted” to act in tempting and trying the good.

And touch his bone— See the note at Job 1:11. Afflict his body so as to endanger his life. The words “bone” and “flesh” denote the whole body. The idea was, that the whole body should be subjected to severe pain.

And he will curse thee to thy face— Notes at Job 1:11.