Well i dont have the answer but i do have some tips
Looking at the word, what are some of the key things that come to mind:1. Mystery of life in general- stars, planets, galaxies. Why are we here? What brings us here?2. Mystery of a movie - the suspense which comes out in the end3. Mystery of someone's life in particular - Subhash Chandra Bose's life ended up with a mystery4. Mystery puzzles and murders - Sherlock Holmes stuff5. Any personal life story which had mystery element in it, a story from childhood etc.6. What is mystery? Why mystery is important? They say necessity is the mother of invention. Even before that, mystery is the mother of the idea of inventing something at the first place.You can combine these factors in one or more ways and come up with a short speech on mystery.