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 description of the situation and answer the directors gave to the question on Nala's father:
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