There is a slight difference in meaning between "Can money buy happiness?" and "Does money buy happiness?" 1."Can money buy happiness?" This question is asking about the possibility of money being able to buy happiness in general. In other words is it possible for money to bring happiness? 2. "Does money buy happiness?" This question is focuses on the reality of whether money actually buys happiness. In reality, does money lead to happiness? Even though the way you asked the question is correct and could be understood by anyone, this version sounds more natural when asking for a comparison. "What is the difference in meaning between these two questions?" Hope this answers your question! This version sounds more natural when asking for a comparison.