Doubts in salaah

To the best of his ability, he should make taharree (try to remember) whether he had recited the dua-e-qunoot. If the dominant portion of his mind is that he had recited it, then he will not have to make sajdah sahw at the end of the salaah. However, if the dominant portion is that he did not recite it, or there is no dominant feeling that comes in his mind and his mind remains unsure, then he should make sajdah sahw at the end of the salaah.

And Allah Ta'ala (الله تعالى) knows best.