He asked God to forgive them, for they know not what they do.
Christ didn't pray to himself, he prayed to God, His Father. Christ is not God, nor did Christ ever say He was God. Jesus Christ is the Son of God and not God himself.
He was praying to God, asking,"“My Father, if it be possible, let this cup pass from me; nevertheless, not as I will, but as you will". Even though he was the son of God, he was still human and felt fears like us. I mean He was going to take the wrath and punishment for the sins of all mankind, I'm sure he was wondering if there was some other way. And he didn't know because he wasn't all knowing either. He had to learn everything by the Holy Spirit and God.
He didn't, he prayed to his Father the one we call God
to forgive the ones who were crussified him