The source is this article (The New Yorker).
He has an affectionate but difficult relationship with his girlfriend, Sophina (Melonie Diaz), the mother of his young daughter, whom he adores.
To which person this whom refers? What are the basic rules/conventions for using it?
Answer
I would say whom refers to daughter, because it is mentioned already that he has an affectionate but difficult relationship with the mother, which obviously is less than adoring; besides, the relationship was mentioned already. So even if grammatically it is unclear, logically makes sense.
Attribution
Source : Link , Question Author : Graduate , Answer Author : Theta30