For blogging, use the same topic in which you are an expert. First of all, remove from your mind that when will I start earning money from blogging. You should pay attention to the fact that I can write as much as possible. If you do not have much knowledge about a topic and its search volume is high. So you will think why should I write about this topic. But because you do not have much knowledge about that topic, you cannot write well about that topic. So my advice is to hold one topic in which you are an expert.

Yes, if you want to find keywords and know what the search volume of that keyword is, then you can use a tool, whose name is:

Google Keyword Planner