I did a little experiment with H.'s suggestion that inflection might matter with wh- questions. T. and I were playing stairway catch with two balls, but he only returned one ball sometimes. When I didn't see the other ball for a few rounds, I asked, "Where is the other ball?" making sure to rise at the end. He didn't answer verbally, but both balls came down the stairs in the next round.
So he _does_ understand at least some wh- questions.