There are three areas in which to compare and contrast the two works: The historical, the production, and the aesthetic. The last one is the most ambiguous and subjective, therefore, it is advantageous to look at the historical first.
Note the historical setting for Da Vinici: Who were the patrons of art and how did that affect the artist's work? Who commissioned the portrait in this case? What was the political-social culture of that time and did it influence the production of the painting? Was Da Vinici making a "statement" about his political-social frame or did an artist of that time have that option?
Now compare that to the time frame for Warhol's work. Was this a commissioned work and would that be an influence in the rendering? Was Warhol making a "statement" about his political-social setting? Was he looking into the aspects of the current culture with this image, and ...
Compare and contrast Leonardo Da Vinci's "Mona Lisa" to that of Andy Warhol's "Marilyn Monroe"