As you work through the article, notice where the author cites arguments or evidence.
When you find points where an author seems to disagree with another source, or when an author seems to be building upon previous sources, go find those.
Here are some ways to do that:
Copy and paste the citation, in whole or in part, into the search bar on www.lib.utexas.edu
Or, do the same on Google Scholar which also allows you to see who has cited the paper you're reading and how they have built their own research upon it: