There is no one “magic” way to find the best dissertation topic, but some ideas here may help you to decide the kind of thing you are interested in.
One great way to know what is current in research is to either go to a conference (if you can afford the time and money) or find suitable conferences and see what the “call for papers” suggests. You can also look back to previous years to see the topics and areas that people were working on. Some of the conference papers will eventually become a published paper or book, so it’s worthwhile knowing titles and keywords.
EDULearn conference https://onlinell.wordpress.com/2016/02/16/edulearn-conference-2016/