This question assumes that extraterrestrials are some form of intelligence similar to our own, with whom we could communicate physically, mentally, emotionally, verbally, in writing, rationally, and consciously. After all, you cannot really ask a question to a life form such as a plant, a bacterium, or sensory waves that we are unable to understand. I think it is important to be clear about what we mean by “extraterrestrial” here.

With that in mind, if we were able to ask a question to an intelligent life form that did not originate on this planet, I would ask only the great philosophical question that humanity has pondered ever since conscious thought first emerged:

Why?

Why is there something rather than nothing? Why do we exist? Why does consciousness arise? Why does the universe seem to seek understanding through us?

And if they don’t know why either?

Then they’re not exactly the kind of intelligent life form I’d enjoy spending my time with.