Pointing towards the photograph of a person, Saksham said, "She is the only daughter of the only daughter of my father". How is Saksham related to the person in the photograph?

Let's break down Saksham's statement:
"The only daughter of my father" → This is Saksham's sister.

"She is the only daughter of [Saksham's sister]" → This means the person in the photograph is Saksham's sister's daughter (Saksham's niece).

Since the person is Saksham's sister's daughter, Saksham is her Mother's brother (maternal uncle).