It is returning a list because you have selected ‘All’ instead of ‘First’ at the Range option. All can possibly return multiple object (aka a list). If you change it to’First’ then you can use $NaturalPersonData/FullName (if FullName is the attribute that the user fills in, I can’t tell from the screenshot).
As the name suggests: All will return all objects in the database of type NaturalPersonData, you can use a XPath Constraint to narrow down the search.