Use search tools that limit by "peer review." Standard library research databases that make it easy include:
Serves as the central resource for researchers at all levels. Covering more than 160 subjects areas, ProQuest Central is the largest aggregated database of periodical content. This award-winning online reference resource features a highly-respected, diversified mix of content including scholarly journals, trade publications, magazines, books, newspapers, reports and videos. *This is a Traveler resource. The Traveler Statewide Resource project was made possible in part by the Institute of Museum and Library Services.
Cross-search the content of multiple Gale databases (including the content of Gale eBook titles) at one time through a streamlined, common user interface. Filter by source type easily using tabs to limit to Academic Journals, News, Images, Videos and more.
On the journal's official web site, the publisher should clearly state if the journal is peer reviewed. It may take some looking. You should also be able to find this in the beginning of the journal itself, if you can get the PDF or a print copy.
Search the name of the journal (not the article's title). Try Google or NWACC's official directory to see if it's Refereed:
Check with your instructor or ask a librarian.