Agree with @pdavis. To expound a little:
If you're using AJAX and the content type you're sending back is JSON, you don't need to do anything. Assign the response to a variable and use as a normal object. (e.g. response.participants.Designation)
If your content type is not JSON, then you'd use something like this to turn it into JSON: var response = JSON.parse(myResponse);
Then, you could use it like a normal object (e.g. response.partipants.Designation).
If you're looking to display the value of a JSON object's property, that's where stringify can help. For example: console.log(JSON.stringify(myResponse)).
That said, Chrome can now display a JSON object in the console without a problem. This didn't used to be the case. It used to be you needed to use JSON.stringify. Now, you don't, and it will display the JSON object as an expandable tree.
Also, little trick... use jsonlint.com to paste your JSON in to make sure it validates okay. It's a great tool.