How do I check particular attributes exist or not in XML?

You can actually index directly into the Attributes collection (if you are using C# not VB):

foreach (XmlNode xNode in nodeListName)
{
  XmlNode parent = xNode.ParentNode;
  if (parent.Attributes != null
     && parent.Attributes["split"] != null)
  {
     parentSplit = parent.Attributes["split"].Value;
  }
}

Just for the newcomers: the recent versions of C# allows the use of ? operator to check nulls assignments

parentSplit = xNode.ParentNode.Attributes["split"]?.Value;

If your code is dealing with XmlElements objects (rather than XmlNodes) then there is the method XmlElement.HasAttribute(string name).

So if you are only looking for attributes on elements (which it looks like from the OP) then it may be more robust to cast as an element, check for null, and then use the HasAttribute method.

foreach (XmlNode xNode in nodeListName)
{
  XmlElement xParentEle = xNode.ParentNode as XmlElement;
  if((xParentEle != null) && xParentEle.HasAttribute("split"))
  {
     parentSplit = xParentEle.Attributes["split"].Value;
  }
}