Problem: If you start proving to people from the past that you have come from the future, using scientific discoveries that will be new to them, then this can greatly affect your current reality. We need to look for alternative ways.
to show how to make gunpowder and a Kalashnikov assault rifle, to be known as a weapon genius and to settle under the wing of the current rulers. further, as an option to open electricity and magnetism to people, if it has not yet been discovered, and to show that more weapons can be made with it. even if you are recognized as a sorcerer, then the current rulers can turn a blind eye to this if you show them the opportunity to bend competitors optionally tell the principle of the internal combustion engine or, at worst, a steam engine (boiler)
In general, it seems to me not important to prove the very fact that you are from the future, without real proofs that can be applied in practice, no public recognition can be achieved
If even without knowledge, for example, about historical events, then nothing, but if there is such knowledge, then through predictions you can convince, but if the events that you know about are rare, then life may not be enough for this. Well, and the main time directive - predictions can change the chain of events and then the predictions end, at best.
This is a great question, and there is a great variety of it on Quora, for example https://www.quora.com/How-would-you-prove-you-were-from-the-future-if-you-found -yourself-in-Middle-Ages-Europe.
And as it is correctly noted there, if you get into the Middle Ages, then nothing. That is, someone will believe you, while someone will continue to consider you a member of a secret order, a messenger of the devil, or substitute it to your liking.
But if you travel from the future to at least the 19th century, and at the same time are an expert in something more useful than comparative literature, there are chances. All ways of demonstration are carefully sucked into the cinema. The most reliable are knowledge of history, technical or natural sciences. And stories in any form - error-free sports betting can also convince someone. Answering scientists to the questions that torment them is generally excellent.
But the best thing - even more so if you've really decided to travel through time naked and empty-handed - is to be able to replicate the experiment. In this case, you can send some scientific authority back and forth for 5 minutes, and then he will quickly convince the general public. Of course, if everything goes well, there will be no two of them, no one will step on a butterfly, a singularity will not happen, or a black hole will not open up that will suck the general public into the jo ... well, in general, we do not know where it can be sucked.