Where can we change the reply to address of the email notifications in Web TimeSheet ?

You can change the "Reply to:" address of the email notification by editing the email notification.

Click 'Administration' icon

Click 'E-mail notifications' under Communications category on the left hand panel.

Click 'Edit' and change the "Reply to:" address to whatever you want it to be.

By default it will be wts@yourcompany.com.