Showing a medieval knight the election of the prime minister of Malaysia in the year 2072 may be a safe.
I don't think even this idea would be safe, as the showing still changes the attitudes of the knight you could bring about the concept of democracy early in a feudal based society. This in turn could affect the prime ministers campaign and subsequent election. The only way to be sure that a small change in the past does not mess up the future indicated is to make sure that the two time periods cannot be related at all. If instead you showed the knight the election of the alien prime minister of a planet as at most many years in the future as light years away it might work. This is dependant on no causal relationship being able to travel faster than light
Even then we would have to make sure the knight couldn't perceive or understand what they are seeing. It needs to be not only alien but incomprehensible.