Do we know where the land of Nod (Gen 4:16) was?

No, we have no clue. Nor do we have any notion where the city of Enosh might have been. It was east of Eden, and if Eden were in northern Mesopotamia, then perhaps it was in southeastern Mesopotamia, near where some of the oldest Sumerian cities were. But we must also bear in mind that this was before the Flood, and therefore all such geographical speculation becomes silly; the terrain itself might have changed immensely.