There is no official information, not serious information anyway. As in someone once asked this from the first movie's directors in the 2004 Reunion but the directors didn't bother to give a serious answer but only joked around and gave half-assed joke as an answer.
As in it is quite clear the film makers never cared and still do not care to decide her father's identity. It appears they want to leave it up to fanfiction.
Here's a transcript of the 2004 Reunion, including detailed descripción of the situation and answer the directors gave to the pregunta on Nala's father: link
Nala's father isn't Scar. There is a new breakthrough that shows a cave drawing of Nala's dad on the lion guard. He looks like Kion does. Kion is also Similar to mufasa. I'm not suggesting that Mufasa is o is not her father. I'm simply saying he is proved to not be Scar.