id   username     useraddress   location  comments
1    explename    expleaddre1   va        *NULL*
2    explename2   expleaddre2   ma        mycomments
3    explename3   expleaddre3   la        mycomments
4    explename4   expleaddre4   ka        mycomments


 SqlDataReader dr = cmd.ExecuteReader();

        while (dr.Read())
        {
            lbluserid.Text = Convert.ToInt32(dr.GetString(0)).ToString();
            lblusername.Text = dr.GetString(1);
            lblusertitle.Text = dr.GetString(2);


            lst.Add(unt);
        }

        conn.Close();

int ordinalPos = reader.GetOrdinal("Comments");
if(!reader.IsDBNull(ordinalPos))
{
    labelComment.Text = reader.GetString(ordinalPos);
}
else
{
    labelComment.Text = "No comments found!";
}

public static class SqlDataReaderExtensions
{
    public static string GetString(this SqlDataReader reader, string colName, string defIfNull)
    {
       int ordinalPos = reader.GetOrdinal(colName);
       return (!reader.IsDBNull(ordinalPos) ? defIfNull : reader.GetString(ordinalPos));
    }
}

labelComment.Text = reader.GetString("Comments", "No comments found");

using (SqlCommand command = new SqlCommand("SELECT * FROM YourTable", connection))
{
    SqlDataReader reader = command.ExecuteReader();
    while (reader.Read())
    {
       string comments = reader.GetString(4);
       if (comments != null)
           Console.WriteLine("Comments is {0}", comments);
       // Assign Text property of your labels..
    }
}