If you encounter someone claiming to be a time traveler from the future, it can be challenging to devise a single question that definitively proves their authenticity. However, you can try asking a question that requires specific knowledge or details about the future that are unlikely to be known to someone in the present. Here's an example:
"What significant event will occur in the next year that is completely unknown to the public and has not been reported in any news sources or publicly available information?"
By asking for a specific event that hasn't been reported, you're testing their ability to provide exclusive information about the future. However, it's important to remember that people can make false claims or predictions, and simply providing an accurate answer to a single question doesn't necessarily prove someone's status as a genuine time traveler.
When evaluating such claims, it's crucial to exercise critical thinking, consider alternative explanations, and examine the evidence and consistency of their statements. Extraordinary claims require extraordinary evidence, so it's always wise to approach such situations with skepticism until substantial proof is presented.