No one. God has been God from all eternity. He is uncreated.
It doesn’t sound like Soc was playing with words. He was engaged in a Socratic dialogue with poor E. Howe, probing and asking the important questions. If, as Joseph Smith taught and declared to be doctrinal, God was not God from all eternity, but worked out his own salvation with fear and trembling, then it’s a fair question to seek to know God’s father, and his father’s father, and so forth until we finally reach the penultimate God, uncaused and eternally God. That is, unless there is no uncaused God, just an eternal chain of uncaused causers. Those are the only two possibilities that logically follow from Joseph Smith’s authoritative teaching. Remember, he taught it to be doctrinal and staked his prophetic authority on its truth; for Joseph, God was not God from all eternity but worked out his own kingdom with fear and trembling, just like us. Who then was God’s heavenly father (and Jesus’s heavenly grandfather?)? And so forth. I think Soc asks a fair question.
NS