Has Trump ever commented on Biden yet?
Good question.
Not sure.
I don’t specifically recall him saying anything substantial on Biden but I think research is needed here to specifically answer that.
Here is the only thing I have seen Trump say about Biden so far and it is complimentary,
http://www.washingtontimes.com/news/2015/aug/2/donald-trump-joe-biden-would-do-very-well-in-presi/