Comments field in dojo calculation script
One answer
Please see https://jazz.net/wiki/bin/view/Main/AttributeCustomization#Accessing_built_in_attributes_of for the documentation and the list of supported built in attributes. Note that the work item comments are neither an attribute - it is in fact not an attribute based implementation - nor are they listed in the JavaScript API.
Also see https://jazz.net/library/article/1003/ for a nice over all introduction.