Which religion is right?
This is a question that can never be answered with certainty, at least not while we are alive on Earth. It is generally impossible to prove that any religion is right or wrong. Of course, we can prove that individual religious figures are right or wrong if they make predictions about what will happen in our world, but it is not possible to know whether, for example, Christianity is right and Islam is wrong or vice versa.
We cannot know if a religion is right or wrong because we cannot prove or disprove its major beliefs. We cannot prove the existence of God at all, so we certainly cannot prove that God is or is not made up of three separate beings (who are, at the same time, one) as Christians believe. We cannot prove that God exists so we certainly cannot prove that he sent an angel to transmit the Koran to the Prophet Muhammad.
We also cannot appeal to human logic. We know that people generally tend to believe that the religion they are brought up in is the right religion. If all human logic pointed to the truth of a given religion, then surely most people who were exposed to that religion’s ideas would convert to it. But that is not what happens. Instead, people stick with their own religions and reject other religions simply because they have grown up with their own religion and have been trained to believe it is true. Thus, when we try to use logic to discover which religion is right, we will typically fail because our logic is clouded by our own conditioning (and because there is no logical way to prove that one religion is superior to another).
Many people would answer this question by saying “of course, my religion is right.” However, they cannot prove the rightness of their religion because it is impossible to prove that one religion is right and the others are wrong.