If you haven't heard of this idea before, please note that I completely borrowed this idea. Annie Fetter did an Ignite about it a few years ago.
When you just ask kids what they notice and what they wonder, you are really helping them to understand that they already have mathematical ideas going on in their mind. The other great thing is that every student can participate right away. No matter their skill level, students notice and wonder things. There are no "fast finishers" yelling "DONE!" and students that struggle can contribute as well without fear of being "wrong."
I loved using this structure with my students last year. I generally used it as a warm-up/bellringer with a variety of prompts. The one above is a graph that is very visual with pictures of food on it. Here are some other ideas for prompts: