There is no information about the CheckmarkBlock object in the XML output.
FineReader Engine does not currently support the field-level export scenario for the XML output.
Recognition results for a checkmark can be accessed via the corresponding CheckmarkBlock object and its properties CheckmarkState, IsSuspicious, and AmountOfBlack. The properties are available after the Process or Recognize method call.
It is possible to export the values of the CheckmarkBlock properties by implementing a custom export algorithm that will be able to write these values into an XML file.