Hi there i would advise you to use tools like https://answerthepublic.com/ also, you can use Keywords research and search the info; Look at the facebook groups and ask the people if they are interested in your topics and if they would pay for it. Another tool i would like to use to determinate if a niche is profitable is looking in youtube and use this plugin called TubeBuddy which gives you a bunch of info about the title; the Seo; the research and you can use all that info to realize if your it's profitable or not.
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