Your father's brother's son's daughter is your second cousin.
God
granddaughter
Your father's brother's son is your first cousin and your daughter's second cousin.
My son. "My fathers son" is myself, if I don't have brothers and sisters.Therefore, "A certain man's father is my father's son" simplifies to "A certain man's father is myself".
That means that the man in the photo is his son. "My father's son" is himself (since he has no brothers and sisters); since he is the father of "that man", it follows that "that man" is his son.
his son
The person in question is your son. Think about it this way: Who is "your father's son"? It's you, because you have no brothers or sisters. So, you just replace "your father's son" with "you", and the riddle now reads: "...that man's father is you." Simple.
your 5th cousin
The father's son is the uncle of the son of the father's daughter.
His son.
cousin!
Your first cousin.