Kavita,

there is no way using JavaScript. Although you can create Java based Attribute customization as described in http://rsjazz.wordpress.com/2013/06/26/attribute-customization-java-based-value-providers-conditions-and-validators/ , I am not completely sure if that can provide you with the API you need. Also, the question is when this gets triggered. A calculated value only gets triggered if the dependent attribute changes. Since a parent link is a link and not an attribute I doubt that would trigger the customization.

Default values are only triggered on creation of the element. Since when you create a work item, there is no parent link yet, and a lot of other data is not yet available, default values are limited in what they can do.

Nevertheless, a participant could do what you want, to some extend. Just not on creation. You could provide an advisor that prevents from saving if there is no parent. You can provide a participant that enters the values on the first save. The participant would look at the new reference to the parent.

You should not attempt to use the advisor because of http://rsjazz.wordpress.com/2012/12/14/do-not-modify-the-triggering-element-in-an-operationadvisor/ and I also don't see the advantage, an advisor works on save as well.

Worst case you can enter a specific state that you have to get over and requires the data.

One question for me would, how do you know you need a parent work item?