Hi,
Create a variable (named VarWithMyLink for example), and assing the variable a link on preparation or where you load de data. And try this:
var contentString = '<a href=\'" + VarWithMyLink + "\'>Click Me</a> <h3 style=\'margin:0\'>"+GetUser(GetPotholes.List.Current.PotholeNotification.UserId).User.Name+"</h3><br><strong>Address:</strong><br>'"+GetPotholes.List.Current.PotholeNotification.Comment+"';