What was David Rubin's job in the movie "Days of Thunder"?
"Days of Thunder" refers to title = 'Days of Thunder'
SELECT T2.job FROM movie AS T1 INNER JOIN movie_crew AS T2 ON T1.movie_id = T2.movie_id INNER JOIN person AS T3 ON T2.person_id = T3.person_id WHERE T3.person_name = 'David Rubin' AND T1.title = 'Days of Thunder'