What was Voltaire asking (what was his main question) in Candide?

In Candide, Voltaire is questioning whether the philosophy of optimism is a viable perspective on the world, given all of the tragedy that occurs every day. Voltaire satirizes this philosophy in his novel, mostly through the character of Pangloss, who is a caricature of Leibniz, proponent of optimism during Voltaire's time (Age of Reason). The philosophy holds that we live in the best of all possible worlds and that everything is for the best; everything tragic that happens is not a result of a malevolent god but rather a natural product of human free will. Every tragedy is part of something bigger, and whatever is bigger is ultimately for the greater good. Having witnessed catastrophic events like the Lisbon earthquake and the Seven Years War in his lifetime, Voltaire simply could not believe in this philosophy. 

In Candide, Voltaire answers the question of whether optimism is a viable philosophy by exposing how ridiculous it is that a person can hold this perspective in light of all of the destruction, death, pain, and loss in the world. At the start of the novel, we see that Candide, a naive young man, has obtained all of his education from Pangloss, his tutor and a philosopher who uses any twisted or exaggerated logic he can to justify his optimism. At the end of Chapter I, Candide gets expelled from Westphalia and embarks on a quest on multiple continents in search of this "best of all possible worlds" that Pangloss has taught him exists. Candide repeatedly finds that there is endless corruption and suffering in the world. Voltaire uses hyperbole throughout the text to emphasize that it is impossible to feel optimistic under the circumstances he has his characters endure. It takes him a while, but eventually, Candide gives up on Pangloss's philosophy and instead embraces pragmatism; at the end of the novel, Candide simply wants to tend his garden, or immerse himself in practical work. Upon finishing the novel,  the reader should see that Voltaire believes optimism is not a logical philosophy; those who continue to cling to it are set up for ridicule in Candide.