1. mailMsg.CC.Add(ConfigurationManager.AppSettings["EmpCC"].ToString());
2. <add key="EmpCC" value="EmailId" />
3. Text='<%# Bind("EmailId") %>
Based on following three, it's clear that the way you are trying to use EmailId field is incorrect. Hence, the cc field is not correctly populated to get an email.
Your 'cc' field is getting data from a grid so you need to pull from there instead of forcefully using(copy-paste 'to' logic!) Web.Config.
If you have a grid Ui where every row has some button to send an email then use the grid row to get the 'cc' email id and use it in code. Or else track the email id any other way to pass on to email method. Web.config method is surely not the way.