Job 12:9 - Ellicott's Commentary On The Whole Bible

Who knoweth not in all these that the hand of the Lord hath wrought this? — This is the only place in the dialogue parts of Job in which the sacred name of Jehovah is found, and Job’s very use of the word in such a context is the clearest evidence of the superior knowledge that he claims. No one of his friends makes use of the name; but Job uses it here, and shows thereby his knowledge of the covenant name.