. . . . . . . . questions Ann asked always seemed to be . . . . . . . . questions to which Paul knew . . . . . . . . answers.

In the first blank, article "the" will be used because here questions are definite (asked by Ann).
In the second blank, "no article" or zero article will be used because no article is used to refer to something already known.
In the third blank, article "the" will be used because here the word 'answers' denotes a definite term.