Start with reading this:
http://cognospaul.com/2013/02/18/cognos-mashup-services-a-brief-example/
It has an example of a method of running a report in JSON format and using the results in JS.
http://cognospaul.com/2013/02/18/cognos-mashup-services-a-brief-example/
It has an example of a method of running a report in JSON format and using the results in JS.