Put your domain in there it will show you results of all similar content sites.
Then you manually look at them. It highlights the similar contents.. Some results will not be that much.. Others will have a lot of your contents.
I have found sites that copied my whole page that i put in copyscape to check, or copied main parts of my page..
Second step.. How to prove it was your contents.. Well archive.org can show who’s contents was there first. This is all good information to prove legally who copied whom.
It is illegal to copy someones orginal words or graphics without permission.
General idea’s of site layouts you can not do much about.
Usually you can ask the person to remove contents and they will.. If they do not you can contact affiliate program managers, which most are helpful on this as well.