Hi ramco1917,
If you are generating HTML then you need to append br tag.
This will add a break and create a new line for the html.
StringBuilder sb = new StringBuilder();
foreach (var colum in Result)
{
sb.Append(book);
sb.Append(" has been done by ");
sb.Append(colum.Name);
sb.Append(" dated : ");
sb.Append(Convert.ToDateTime(colum.SessionDate).ToString("dd-MM-yyyy"));
sb.Append("<br/>");
}