#1 Why is something right or wrong?
Atheists may believe something is right or wrong, they may even live very moral lives, but they cannot give you a reason to do what is right as opposed to what is wrong. If there is no God, then there is no objective standard of right and wrong. If there is no Law-giver, there is no transcendent Law. Steal, kill, and lie...or don't, whatever you choose.
#2 Why is human life valuable?
An atheist may tell you that human beings are high-up on the food chain, even that they are complex and intelligent. But they cannot offer a reason why human life is more valuable than any other animal, insect, or even plant life. Then again, what makes living beings more valuable than non-living objects, like a rock? Or non-living objects more valuable than nothing at all? In fact, the idea of anything having 'value' must be ousted from an atheist perspective (You can say something is valuable for survival, but not inherently valuable, as survival is no more valuable than extinction).
#3 What is the purpose of life?
An atheist can tell you what he or she personally feels about life (do good, love people, save the environment, etc.), but there is no objective purpose to life. We exist as a result of chance and time. No purpose, no meaning, no real significance to life. An atheist may live a life of love and compassion, but there is no objective reason for doing so, and certainly they cannot speak meaningfully against others who choose to use their lives to do otherwise.
#4 What makes music, art, and poetry beautiful?
An atheist may love music and art and poetry, but there is no transcendent significance to them. They do not add anything to our survival instincts. They are superfluous...unless there is something in us that rises above just physical nature. If not, it is completely relative. Eric Clapton is no better than me strumming my guitar, Van Gogh is equal to a 1st year art student, and Shakespeare is as beautiful a poet as anyone else. Beauty is ONLY in the eyes of the beholder. Or did God place a love for beauty in good music, art, and poetry in our souls?
#5 Where did we (matter) come from?
I know different answers have been attempted, but seriously? The two answers that are given are both unscientific and nonsensical: 'We came from nothing' and 'We always existed'. I'm not sure which is worse: that the universe could spring into existence out of absolutely nothing or that matter existed for all eternity. Go back a trillion years and there it is! Go back a trillion times a trillion years, there it is! Go back a 1 with a trillion zeroes after it and there it is! Keep going and going and going and still there it is!
(Some might respond: but where did God come from? Christian theology has always taught that God does not exist within our universe and thus is not subject to the cause and effect physical world that we live within. He is transcendent, other than us. He is the unmoved mover, as Aristotle and Aquinas labeled Him. In our universe every effect must have a cause, but Christians have never said God is subject to our universe. He is its Creator. Thus God's infinity is not nonsensical, just difficult to imagine. If we said God is part of this universe and always existed, then we would have the same problem.)
#6 Where are we headed?
Well, actually there is a sort of answer atheists can give to this: extinction. It is absolutely inevitable from an atheist framework. It may happen in 10 years, 100 years, 1000 years, a million or more, but it will be the ultimate end of human life. No matter what we say, do, think, eventually we will be extinct. Eat, drink, and be merry now, because this is all there is. The future is lights out utter darkness.
#7 How do you know there is no God?
The only way you could know with certainty that there is no God is for you to have infinite knowledge of the universe. This is true of all absolute negatives. It is like saying "I know there is no such thing as a 5 legged dog in this universe." The only way I could know that with absolute certainty is to have complete knowledge of the universe and every dog within it. In other words, the only way to know there is no God is to be omniscient, which can only be an attribute of God himself. Funny, the only one who can know that there is no God would be God himself! This is why many atheists now call themselves 'agnostic.' Agnostic usually practically means "I don't know, but I am going to keep living as if there is no God."
On the flip side, an absolute positive is different. I don't have to have infinite knowledge of the Universe to know my wife exists. I have experienced a genuine relationship with her. To be a Theist (to believe there is a God) only requires personal knowledge of Him, something that many (most?) human beings have experienced since all of recorded history!