Step 1: Go to the profile of the user in question!
Step 2: There you will see More option, it is just beneath the tab that reads Add as a Friend.
Step 3: Go for the Ignore User option and click on it.
Step 4: Release G talk and then opt for Settings option.
Step 5: Click on Blocked Users and your computer will show you all the blocked contacts. From that list of contacts you can find out the e-mail address of that person.