What does Schindler want the Jewish workers in his factory to make?

He wants them to make faulty shells for the Nazis.

Schindler has the Jewish prisonors do everything because he has to protray a good German that is for the war effort. If he gave any inclinatation that he was trying to save the slave labor, he could possibly be killed with his workforce. Throughout the movie, in a subtle way, he bought the SS with lavish gifts. He was able to get their trust. As in the answer above, the Jewish workforce had no clue he was making faulty shells. It was only a rumor that he was messing with the calibration on the machines.