Your question is too broad and unclear. There are commentary articles on every field and on many different topics. It is not possible for me to provide any examples without knowing your field. Commentaries usually draw attention to or present criticism on a previously published article, book, or report. If you have enough knowledge about your field, it should not be difficult for you to write a commentary.
To find examples of commentary articles, the best person to ask would be your librarian. He/she would guide you to popular journals in your field that publish this type of article. You can then go through previous issues of these journals and look for commentary articles.
You can also go to Google Scholar and use "commentary article" along with the name of your field as keywords. The search results will show commentary articles in your field.