If I had the opportunity to interview an extraterrestrial being, my first question would be:
"What is the most significant piece of knowledge or wisdom that you wish to share with humanity?"
This question aims to seek insights or information that could have a positive and profound impact on our understanding of the universe, our place in it, and how we can improve ourselves and our world. It allows the extraterrestrial being to share their unique perspective, knowledge, or experiences, which might be far beyond what humanity currently comprehends. It could open up new possibilities for growth, cooperation, and betterment on a global scale.