What you can tutor is dictated by your particular skill set rather than the subjects required by other people.
There are 2 main reasons for this.
Firstly, you need to have a passion for the subject and the ability to transfer your love and knowledge of the subject to someone else.
Secondly, the world is a huge place and the people in it all have different requirements. Regardless how niche the subject that you want to teach is, there will probably be someone needing support with it.