Annie Fetter, of Math Forum fame, did an incredible Ignite Talk at NCTM one year entitled "What Do You Notice or Wonder" and it really opened my eyes to the power of observation & wondering. I share it here as a here as inspiration to help you ask the questions that will invoke wonder, inquiry and thinking in students.
Additionally, Randall Munroe did a great TedTalk on the question "What If..." that explores a wonderful math/physics problem. Again, to demonstrate the power of a simple question to help engage students in thinking.
These are both examples of how a simple question can open up the math ideas that students have and encourages them to explore to find the answers. Ask a simple question and open up the door!