As an example, in the video they chose the topic of insects, with a subtopic of bees. One good open question that could focus the research was "Why do bees work together as a community?" This is a good question because it is open ended, complex, doesn't have a yes/no or one definitive answer, and can lead to deeper thinking.
Thinking about topics, let's assume you chose the topic of dogs, and your subtopic that you want to focus on is dog breeds, specifically. What would be a good open question that would focus your research?