I cannot because I do not understand your problem.
Almost surely, your Plone (apparently some version 5) has
zope.location.interfaces and with it you can find the parent of an object like I have shown in a previous response.
dexterity content types likely implement the
IContained interface directly. In this case, you can use
obj.__parent__ to access obj's parent. The previously described "official way" (explicitly adapting obj to
IContained) is safer, however, as it does not require that obj itself implements
IContained, it is sufficient that it can be adapted to it.