Dost thou know when God disposed them? - That is, the winds, the clouds, the cold, the snow, the sky, etc. The question refers to the manner in which God arranges and governs them, rather than to the time when it was done. So the Hebrew implies, and so the connection demands. The question was not whether Job knew "when" all this was done, but whether he could explain "how" it was that God thus arranged and ordered the things referred to. Elihu asks him whether he could explain the manner in which the balancings of the clouds were preserved; in which the lightnings were directed; in which his garments were warm, and in which God had made and sustained the sky? The Septuagint renders this, "We know that God hath disposed his works that he hath made light out of darkness."
And caused the light of his cloud to shine - That is, Canst thou explain the cause of lightning? Canst thou tell how it is that it seems to break out of a dark cloud? Where has it been concealed? And by what laws is it now brought forth? Elihu assumes that all this was done by the agency of God, and since, as he assumes to be true, it was impossible for people to explain the manner in which it was done, his object is to show that profound veneration should be shown for a God who works in this manner. Somewhat more is known now of the laws by which lightning is produced than there was in the time of Job; but the question may still be asked of man, and is as much fitted to produce awe and veneration as it was then, whether he understands the way in which God produces the bright lightning from the dark bosom of a cloud. Can he tell what is the exact agency of the Most High in it? Can he explain all the laws by which it is done?

Dost thou know when God disposed them - Dost thou know the laws by which they are governed; and the causes which produce such and such phenomena?
And caused the light of his cloud to shine? - Almost every critic of note understands this of the rainbow, which God gave as a sign that the earth should no more be destroyed by water. See Genesis 9:13 (note), and the note there.

Dost thou know when God disposed them, and caused the (l) light of his cloud to shine?
(l) That is, the lightning to break forth in the clouds?

Dost thou know when God disposed them?.... The clouds, that part of the wondrous works of God he was speaking of; when he decreed concerning them that they should be, when he put into them and stored them with rain, hail, snow, &c. disposed of them here and there in the heavens, and gave them orders to fall on this and the other spot of ground; wast thou present at all this, and knew what God was doing secretly in the clouds, and before heard what would break out of them, or fall from them? and if thou art ignorant of these things, canst thou imagine that thou shouldest be made acquainted with the secret springs of God's providential dealings with the children of men?
and caused the light of his cloud to shine; either the lightning to break through the cloud, or rather the light of the sun to shine upon his cloud, prepared to receive the light reflected on it, and form the rainbow; which, as it is called his bow, the cloud in which it is may be called his cloud; which is one of the wondrous works of God, and is called by the Heathens the daughter of wonder (u); formed in a semicircle, with various colours, and as a token that God will drown the earth no more; an emblem of the covenant of peace, and of Jesus Christ, said to be clothed with a cloud, and with a rainbow about his head, Revelation 10:1.
(u) Apollodorus, l. 1. p. 5.

when--rather, "how."
disposed them--lays His charge on these "wonders" (Job 37:14) to arise.
light--lightning.
shine--flash. How is it that light arises from the dark thundercloud?

Them - The things before mentioned, the clouds, rain, snow, and other meteors. Did God acquaint thee with his counsels in the producing and ordering of them? His cloud - Probably the rainbow, seated in a cloud, which may well be called God's cloud, because therein God puts his bow, Genesis 9:13.