What is said when repeating verses such as: "And We have certainly made the Qur'an easy for remembrance, so is there any who will remember?" and "So which of the favors of your Lord will you deny?", and is it obligatory to answer them after each repetition?

It is recommended for someone who recites verses that contain questions to answer them. So, if he recites: {Is not He able to revive the dead?} he should say: "Glory be to You, yes indeed." And if he recites: {Is not Allah the most just of judges?} he should say: "Yes, and I am one of the witnesses to that." And if he recites: {Then which of the favors of your Lord will you deny?} he should say: "We deny none of Your favors, O our Lord, to You be all praise." Other verses can be responded to similarly, as appropriate. For example, to {Is there any who will remember?} one can respond with: "O Allah, make us among those who remember," or "O Allah, help us," or "There is no might or power except with Allah," and so on. This recommendation applies both inside and outside of prayer.