1. If Allah ﷻ knows everything, then why does He put humans through tests and difficulties only to punish or reward them for actions that He already knows they will commit?
True, Allah ﷻ already knows what His creatures will do before He creates them, but still He wishes to actualise that. While His knowledge before the fact is the same as His knowledge after the fact, a change has taken place in what is known. He created to make actual what was potential. Allah ﷻ states in His Book,
وَمَا كَانَ لَهُ عَلَيْهِمْ مِنْ سُلْطَانٍ إِلَّا لِنَعْلَمَ مَنْ يُؤْمِنُ بِالْآخِرَةِ مِمَّنْ هُوَ مِنْهَا فِي شَكٍّ
“He [Iblees] did not have any power over them; however, [We let him tempt them] that We might know who believes in the hereafter and who doubts it.” [34:21]
2. If Allah ﷻ knows everything, doesn’t that imply that humans have no choice and everything is determined by Allah’s knowledge?
No, Allah’s prior knowledge does not compromise our free will. His knowledge is accordance with our choice, not the other way around. Although it may perplex us how Allah ﷻ can have prior knowledge, it also perplexes us how He can create something out of nothing. Our inability to imagine the Divinity and His attributes, does not preclude their reality.
3. If Allah ﷻ is all good and all powerful, why does He permit suffering and devastation to be inflicted on humans?
Allah ﷻ did not create the world for our comfort but rather to test us, and this purpose requires the existence of evil in the world. Those that suffered evil but died in belief will be greatly recompensed for what they suffered, while those that worked evil and died in disbelief will be severely punished. Evil is only a problem for those who ignore the fact of the hereafter.
4. If Christians live pious lives, how can we expect them to be punished for not believing in our religion?
Allah ﷻ has brought everything out of non-existence; thus, He owns everything He created utterly and absolutely. Human beings, on the other hand, only own things in a provisional and dependent manner. Injustice is only the misuse of what does not belong to us, so it is inconceivable that injustice might be predicated of Allah ﷻ. It is a fallacy to suppose that human injustice might be predicated of Allah ﷻ.
Now in the sight of Allah ﷻ, anyone who denies any part of His message has disbelieved in Him, and since the prophethood of Muhammad ﷺ and its finality is part of His message, He considers its denial unbelief, and He has chosen to punish unbelief eternally. Allah ﷻ does what He pleases and though we will all be asked about what we do, no one will have the power or the right to ask Him about what He does. He has declared:
لَا يُسْأَلُ عَمَّا يَفْعَلُ وَهُمْ يُسْأَلُونَ
“He will not be asked about what He does, but they will be asked” [21:23].
5. Can Allah create a stone He cannot lift?
Allah can do anything that is consistent with His being God, not anything that is inconsistent with it. Thus, it is inconceivable that that there could ever be anything He is not strong enough to do. The fact that He created this world shows that His power is infinite.
 Originally I wrote detailed answers covering some twenty pages; however, realizing that most people’s attention spans are very short nowadays, I prepared another version making my answers as short as possible.
Courtesy of DeenGate