"I don't know how to use honorific language."
"Do you know how to make a flight reservation?"
The above two sentences were taken from my homework -- which were graded by my sensei, so these should be the correct translations. My question, however, is why is it that in the first example, を is used, and in the second example, が is used? Is it due to the fact that "わかりません" in this case is being used in the form of an ability? (Potential forms use the が particle.)