You can write a hub on anything. It's not like you write in magazines or newspapers. Here you're focusing on SEO articles and that can be on product reviews or on things or places that interest you. To get ideas, you can do google search on a particular topic. Collect informative points from various websites and re-arrange them in order to maintain the flow.
Please ensure that the websites from which you collect points provide true information. If you've any doubt, you can get books from amazon on that topic. Used books won't cost too much.