Merely asking the question has no particular effect. It has been asked many times without causing any notable consequence -- as, for example, when Dorium repeatedly asked it at the end of "The Wedding of River Song".
What the Silence feared was the question being asked and answered. They believed that "On the Fields of Trenzalore, at the fall of the Eleventh, when no living creature can speak falsely, or fail to answer, a question will be asked. A question that must never, ever be answered." The question is "Doctor who?" & the Silence believed that, if allowed to reach Trenzalore, the Doctor would be compelled to answer with his true name, thus identifying to the Time Lords their home universe, allowing Gallifrey to return & restarting the Last Great Time War.
The Silence were wrong in this belief. The Doctor reached Trenzalore but he did fail to answer ("The Time of the Doctor"). Despite him not answering, Gallifrey eventually returned ("Heaven Sent"/"Hell Bent") but that has not so far (end of Series 10) restarted the Last Great Time War. The Silence were not only wrong but were extremely thoroughly wrong -- wrong in almost every way they could be wrong.