Which Old Testament prophet did Jesus quote the most?
I have not taken the time to make an exhaustive list of every quote Jesus made in the Gospels. But I have found several writers mention that the most quoted books in the Gospels are Deuteronomy and Psalms. Deuteronomy was written by Moses and Psalms was mostly written by David, though there are many psalms written by other authors. It is probably safe to say that Jesus quotes Moses most often.
The question is a bit tricky to answer well because we are told by the writers of the Gospels that they did not record everything Jesus said or did. "And there are also many other things that Jesus did, which if they were written one by one, I suppose that even the world itself could not contain the books that would be written" (John 21:25). So the only way to get a truly accurate answer would be to ask concerning the quotes recorded for us. Next, there is the problem that the four gospel accounts contain considerable overlap. Do we count a quote that appears in multiple accounts as one or multiple? Finally, do we count the allusions or only the direct quotes?