I know what you mean by the sentence, but it sounds very unnatural. A "supposition" is a guess or hypothesis made with evidence. I see the word used mostly in scientific writing and also in formal writing. For your sentence, I would say "Do you have any idea what could have been the reason for this tragedy?" A sentence along the same lines may be "The idea that this tragedy could have been prevented is based on the supposition that he/she was willing to take the proper precautions." "Supposition" is a good word to know, but you will only see it infrequently. Sentences beginning with "Do you have any idea why..." or "Can you guess why..." will be much more common. Hope this helps, J

No this is not used in the correct context. A “superstition” is a belief held without evidence. Usually to do with luck. For example - She would not open her umbrella inside the house, because she thought it would bring her bad luck. She is superstitious. Hope this helps!

The word 'supposition' is correct, however it is a very formal way to express this question. In conversation, or informal writing you would just use - "Do you have any idea what ...."