Type in the title into the search engine that you're considering, or have for your hub. HubPages will populate with all related articles. I've been here for a few weeks now, and can say that it really doesn't matter, as long as it isn't plagerism. You will find that there are many hubs on the same, if not similar content. You can also go to the Forum page, and select a topic that aligns with the subject that you want to write about. In the Forum page you will find many hubbers who write on the same subject.
Just remember that writing is unique for each person, and what you have to offer may be very different, although similar. Each writer may have a different view, and may provide information that another writer didn't.
I hope this helps.