If your xml is like below then you can query it using Linq
var xml = @"<cell>
<cellcontent>
<para>
<paraline>
<string>ABCabcABC abcABC abc ABCABCABC</string></paraline></para></cellcontent></cell>";
var list = XDocument.Parse(xml).Descendants("ParaLine")
.Select(x => x.Element("string").Value).ToList();
list object will contain all value of string element which is inside
ParaLine
element.