"Then Jeremiah said to Zedekiah, “Thus says the Lord God of hosts, the God of Israel, ‘If you will indeed go out to the officers of the king of Babylon, then you will live, this city will not be burned with fire, and you and your household will survive. 18‘But if you will not go out to the officers of the king of Babylon, then this city will be given over to the hand of the Chaldeans; and they will burn it with fire, and you yourself will not escape from their hand....20But Jeremiah said, “They will not give you over. Please obey the Lord in what I am saying to you, that it may go well with you and you may live," (Jer. 38:17-18, 20).
Open theists often state that God displays ignorance of the future by telling people what will happen if they do one thing or another. They assert God doesn't know, and that is why He is laying out the options of what might possibly happen in the future.
When God states "If you do this, then this will happen; if you do that, that that will happen," it does not mean that God is ignorant of the future. It means God is revealing the results of what will happen as a result of various choices. This absolute knowledge of God is possible because God knows all things, including the future and all its options. By contrast, this is not possible with the god of open theism because god doesn't know the choices that will be made, so he cannot tell with certainly what will or will not happen.
Therefore, Jer. 38:17-18, 20 is not displaying God's ignorance of the future. It is displaying God's knowledge of it should certain conditions arise. Given the vast permutations of free will human choices of the future which are not knowable by the god of open theism, absolute certainty is not something the god of open theism can have. Therefore, he could not tell us for certain what would happen. But Jer. 38:17-18, 20 does tell us. Therefore, these verses do not support open theism.