The saveXML is only used if the node has child nodes. In the case of PERSONID then you want the value of the node and woudl use the value property.
In the case of repeating nodes liek you have you woudl use occurance numbers or change your tactic all together and use E4X. The expression in E4X are much easier and more powerful to use. I have included an example of using E4X to get to repeating nodes.
xfa.dataset.data will give you the root of the data dom. I suggest that you put a large multiline filed on the form (this is for debug only) and you can see the structure of the dom in that field. Use this command to populate the field: