Updated Solution.
string[] yourDynamicColumns = { "Column1", "Column2", "Column3" };
string queryFormat = "Select {0} From Employee";
string dynamicQuery = "";
SqlDataAdapter da = new SqlDataAdapter("select COLUMN_NAME from INFORMATION_SCHEMA.COLUMNS where TABLE_NAME = 'Employee'", con);
DataTable dtColumns = new DataTable ();
da.Fill(dtColumns);
foreach (DataRow row in dtColumns.Rows)
{
string columnName = row["COLUMN_NAME"].ToString();
if (yourDynamicColumns.Contains(columnName))
dynamicQuery += columnName + ",";
}
dynamicQuery = dynamicQuery.TrimEnd(',');
string query = string.Format(queryFormat, dynamicQuery);