"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,「が」is used, and in the second example, 「を」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.)