Try asking: “What pronouns do you use?” or “Can you remind me what pronouns you use?” It can feel awkward at first, but it is not half as awkward as making a hurtful assumption.
If you are asking as part of an introduction exercise and you want to quickly explain what gender pronouns are, you can try something like this: “Tell us your name, where you come from, and your pronouns. That means the pronouns that you use in reference to yourself. For example, I’m Xena, I’m from Amazon Island, and I like to be referred to with she, her, and hers pronouns. So you could say, ‘she went to her car’ if you were talking about me.”