Do you know any sites where people can earn extra money writing tips & tricks articles about Wordpress?
there's here - we have a marketplace where you can sell content you've already written or your content creation services.
What kind of content? Are you selling generic content or customized? Have been here long enough to experiment with Sarahk's suggestion of the marketplace... but if you're going for custom jobs like freelance journalism you can always try upwork or some of the other freelancing sites.