Touch, i.e. smite him, not slightly, but to the quick, and to the bones and marrow, so as he may feel pain and anguish indeed, which is oft expressed by reaching to the bones, as Psalms 6:2, Psalms 32:3 51:8.
Related Commentaries of Job 2:5
Job 2:5
5 But put forth thine hand now, and touch his bone and his flesh, and he will curse thee to thy face.