How to send the emails to the developer whos review in DNG is in open state

Sorry, but I am  not able to develop stuff for others for free. It might be not possible to get the data using the reportable REST API, not sure. See the discussion here: https://jazz.net/forum/questions/279779/dng-rest-api-how-to-get-review-data 

My current conclusion is that getting the reviews is only available through a private API.
You might want to raise an enhancement request.

Here the links I found that also mention the private API.

• https://jazz.net/forum/questions/279779/dng-rest-api-how-to-get-review-data
• https://jazz.net/forum/questions/261608/how-to-export-the-review-comments-related-to-artifacts-in-module-context
• https://jazz.net/forum/questions/279337/export-review-comments-from-dng-review
• https://jazz.net/forum/questions/227361/how-to-get-the-reviews-where-a-module-is-used-where-usedin-review-using-the-dng-rest-api
• https://jazz.net/forum/questions/251000/dng-rpe-template-to-publish-a-view-filters-columns
• https://jazz.net/forum/questions/139149/get-the-review-from-oslc-rest-from-rational-requeriments-composer

Once you have the UUID for the review, you can use other APIs to get more data. One example is the reportable REST API where you provide a filter (the UUID) for the review you are interested in.

Please have a look at Ian Barnhards answer in https://jazz.net/forum/questions/279779/dng-rest-api-how-to-get-review-data/279816