You can go to this site ( http://www.duplichecker.com) and copy paste a few sentences into the text box and it will tell you if the content is duplicate or original. http://www.duplichecker.com/
But remember, some hubbers know to change some key words and sentence structure (example of their adding: I think this is the best method....) or (In my experience....) so that the duplicate checker above gets thrown off and content comes up as original.
You can do what I am doing.....although YOU can see the date of your hub being published, the readers cannot. I date every one of my hubs now. Why? Because some people are just plain rude - they read mine and they go and paraphrase it and write theirs a day later. You can "flag" their hub and in option box tell HP why you think it is copied, and see if you can get results that way.
Other hubbers who are more versed in DMCA filings can explain that process to you far better than I. I have had no luck with that avenue. Advice from another hubber told me to make sure I put a COPYSCAPE logo on every hub (DO NOT COPY - THIS WORK IS COPYRIGHT PROTECTED) and I have been doing that.
Before doing that, one of my hubs was stolen almost word for word with very little sentence structure changes, but for a few "I think" and "In my opinion" blurbs thrown in, and that's why it was not a valid complaint for plagarism (duplicate content).
I hope this has been of help to you. Go through the hub forums and you will see other questions about this topic where many others have replied with excellent suggestions.