We are not told and so we ought not to speculate. The emphasis lies not on the giver but on what was given. Yet we need to remember that John receives his revelation in heaven (see Revelation 4:1) and so it follows that the one who gave John the measuring rod was not an earthling, let alone a being from under the earth.
1 Then I was given a measuring rod like a staff, and I was told, “Rise and measure the temple of God and the altar and those who worship there,