Hi Jay, maybe I can help. I might need to better understand the steps you took thus far though. Personally I'd recommend tiles over widgets, but that's a different conversation . Good news is we have an "Ask a Question" widget and tile for either layout. With that in mind, it sounds like you want the content to show in that search bar before they ask, and not ONLY the enterprise search across the entire community, correct? If so, you should be able to edit either widget/tile to only pull content from a certain place. With the widget, I believe it's only documents or discussions/questions. With the tile, we've expanded the options to add additional content types into those type-ahead search results. There isn't a way to have content level permissions unless it's per user (not broad permission model), but we should be able to get the Ask a Question widget working for you.
After you created this new group/sub-space, did you both filter the Ask a Question widget only for that place and also move the piece of content in question into that space/group as well?