Question:

Please, how did Jacob know he was wrestling with God, saying that "I wont let you go until you bless me?"


Answer:

"Then Jacob was left alone; and a Man wrestled with him until the breaking of day. Now when He saw that He did not prevail against him, He touched the socket of his hip; and the socket of Jacob's hip was out of joint as He wrestled with him. And He said, "Let Me go, for the day breaks." But he said, "I will not let You go unless You bless me!"" (Genesis 32:24-26).

When the person Jacob was wrestling with dislocated his hip with just a touch, Jacob had confirmed what he probably already suspected.