How to Parse the XML using FDK?
As you did not get an answer, please allow me to suggest, that giving more detailed background on what you want to do is helpful for the other users in this forum.
Without having more background info on what you want to do, it is difficult to start with giving some help. If want to “parse” XML I suggest to look into XSLT and XPATH. FrameMaker 2019 ships with Saxon Enterprise Edition which is probably the most powerful engine on the planet to do such things. You can plug in an XSLT as a pre- and/or as a post-processing process when opening/saving/closing an XML file in FrameMaker or on an open file in the code view. This makes virtually everything possible.
Alternatively you can use the FDK to manipulate an XML file on the FrameMaker structured document level. As you were talking about tables in a similar post you could use the FDK (or ExtendScript) to e.g. sort the table extract data from it, create a new XML document from it or all kind of other things.
If you give the community here more details, it is more inviting for them to help. Especially in this sub-forum, they are all high-level, busy experts who are happy to give precise answers on precise questions 😉