They are sometimes used to modify nouns when a direct question is not asked, and they are then used, not as interrogative adjectives, but as indefinite adjectives.
I am asking a direct question to which you can give an answer; but if I say, I wonder why you do not study, I have asked an indirect question which does not require a direct answer.
And Nesta, having listened carefully to all he had to tell, put a direct question to him.
Five minutes later, having provided Murgatroyd with rum and water and a cigar, he turned on him with a direct question.
The above list will hopefully provide you with a few useful examples demonstrating the appropriate usage of "direct question" in a variety of sentences. We hope that you will now be able to make sentences using this group of words.