How to get all events from ‘All in one Events calender’ plugin in JSON format?

I had to do the same thing. I used the JSON API plugin and had to create a new controller for JSON API that read the specific data out of the tables that All-in-One created.

Unfortunately there really were not the right calls in the calendar plugin to access all the data (or at least on the older version I used this for) so I had to write the whole controller to do it.

It took only a few hours to do and was pretty trivial once you look at the database structure, so this would be my recommended method to do this.