There are many ways to check the peer-review status of a particular article or journal. One of the easiest ways to do this is to use the library databases and the filters that they provide. For the majority of the databases (including OneSearch), there is an option to narrow down results to only feature results from journals that are peer-reviewed:
The above image shows the "peer-reviewed" checkboxes on ProQuest, EBSCO, and OneSearch databases.
Using these filters can be a great way to ensure that you are only seeing peer-reviewed results.
HOWEVER. It's important to remember that not everything published in a peer-reviewed journal is peer-reviewed. Letters to the editor, book reviews, and editorials all can be printed in these journals without being subjected to the peer-review process.
This method is not 100% reliable, but is usually pretty accurate. If you are looking for complete accuracy, it is recommended that you look up the title in Ulrich's Periodicals Directory.