Do we say ; What is the antonym of or What is the antonym for ? ?

If you say "for" it means it can replace it, which is precisely what an antonym does not do.

You can have a synonym for as a synonym means "the same" and can thus replace the original word.

Your question is unrelated to Air Travel.

Most people would use "of" instead of "for".

The correct preposition in that case is 'of'.

Love is an antonym for hate.  The antonym for hot, is cold, or ugly, depending on the connotation.