XmlDocument doc = new XmlDocument();

doc.Load(filePath);
XmlNodeList cellList = doc.SelectNodes("//Row/Cell");

foreach (XmlNode node in cellList);
            {
                string iNumber = cellList[0].Attributes[0].Value;
                string iAccountNumber = cellList[1].Attributes[0].Value;
                string name = cellList[2].Attributes[0].Value;

string iNumber = cellList[0].Attributes[0].Value;

<Row>
    <Cell ss:StyleID="s69"><Data ss:Type="Number">1</Data></Cell>
    <Cell ss:StyleID="s69"><Data ss:Type="Number">340054288</Data></Cell>
    <Cell ss:StyleID="s69"><Data ss:Type="String">ИВАНОВ  К. С.</Data></Cell>
    <Cell ss:StyleID="s69"><Data ss:Type="String">НОВОСТРОЙКА  28 ГА</Data></Cell>
    <Cell ss:StyleID="s69"><Data ss:Type="Number">271</Data></Cell>
    <Cell ss:StyleID="s69"><Data ss:Type="String">108.8200</Data></Cell>
    <Cell ss:StyleID="s69"><Data ss:Type="String">2015-061195</Data></Cell>
    <Cell ss:StyleID="s69"><Data ss:Type="String">DDS 232</Data></Cell>
    <Cell ss:StyleID="s70"><Data ss:Type="DateTime">2017-09-05T00:00:00.000</Data></Cell>
   </Row>

innerText: 1, argument[0]: s69
innerText: 340054288, argument[0]: s69
innerText: ИВАНОВ К. С., argument[0]: s69
innerText: НОВОСТРОЙКА  28 ГА, argument[0]: s69