May we ask questions on AskUbuntu if we encounter a bug, and we do not know how/where to report it? For example, one can see black screen and is unsure whether he/she should report it against xorg, unity, or whatever else. Is it allowed to ask questions on how to troubleshoot an issue in order to report it as a bug?
Generally yes, but it would be better to as a canonical question such as "How to find out what package to report a bug against". There is a chance your question will be closed as too localised if it's unlikely to be useful for the general audience of Ask Ubuntu.
So, if your specific question is likely to help someone else, ask it! Otherwise it might be better to ask in one of Ubuntu's IRC channels, mailing lists, or the Ask Ubuntu chat.