When distributing the survey, only the emails from email column is picked up.
But yes, if you want a setup wherein you want the email trigger should go to the respondent as well as their manager, then in the contact list you can create a column called managerEmail. Create a ED with same name in the survey. Now either in email trigger or email action, just pipe in this ED(managerEmail) along with respondent email in the "To" textbox, comma separated.

Hi Ron,
Thanks for your feedback and help.
Now, I have a better understanding about EmailTrigger.
My question, now, is how to trigger manager's email, when survey email went out (to either start survey or reminder to complete survey), not when Survey is completed.
Justin