How to fill a combo box with database data

private void button1_Click(object sender, EventArgs e)
      {
          {
              comboBox2.Enabled = true;
              string klijent = comboBox1.Text;
              CON.Open();
              string sqlquery = "SELECT Naziv FROM [Dobavljaci_" + klijent + "] WHERE NazivFirme = '" + klijent + "'";
              SqlCommand cmd = new SqlCommand(sqlquery, CON);
              SqlDataAdapter da = new SqlDataAdapter(sqlquery, CON);
              DataSet ds = new DataSet();
              da.Fill(ds);
              cmd.ExecuteNonQuery();
              comboBox2.DisplayMember = "Naziv";
              comboBox2.ValueMember = "Naziv";
              comboBox2.DataSource = ds;
          }
          {
              string klijent = comboBox1.Text;
              string sqlquery1 = "SELECT stopa FROM NKlijent WHERE NazivFirme='" + klijent + "'";
              CMD = new SqlCommand(sqlquery1, CON);
              SqlDataReader sdr1 = CMD.ExecuteReader();
              while (sdr1.Read())
              {
                  label1.Text = sdr1["stopa"].ToString();
              }
              CON.Close();
          }

System.Data.DataViewManagerListItemTypeDescriptor