How to get users email id

I have configured Zoho signing with gmail. I have a 'Employees' form which has a users filed.I have the appearance of the field to display the email address of the uses. How do I get this user id field in other forms? I am trying to get the email address tied to the user in other forms. When I try to display Employee forms user_id, by default it displays the username and not the email id tied to that user.

Thank you

Anand.