You use *supposedly* to hand on what people say while keeping your distance from it. "He's supposedly the best cook in town." You are not saying he is; you are saying that is the story going around, and your tone usually adds *but I wonder*. It works like the adverb version of "they say that…" or "it's said that…", and it can sit at the front of the sentence, before the verb, or before an adjective. Sometimes the doubt is heavy and sarcastic ("This supposedly waterproof jacket soaked me through"); sometimes it is light and simply careful, the way a polite person marks second-hand information they have not checked. Compare its neighbours: *apparently* leans toward "from what I can see, this seems true"; *allegedly* is the formal news-and-court word for accusations; *supposedly* sits in the middle and is the one you'd use in everyday speech. Say it as four syllables — /səˈpəʊzɪdli/, with the -ed sounded.