Only cite the article you are reading unless the author/s have directly quoted another source and you want to reuse that quote. Then it is best to look for the original source. If you cannot find it, you may cite as a secondary source.
Check primary sources when referring to statistical information or where the author/s are commenting on significant theories, research and so on. It is good practice to refer to the primary source when relevant.
Also look at research which builds on and is conducted after the source you’re reading. Take a look at the Citation Chaining guide for more information.