In sentences such as "We asked the president about the hunt for Osama bin Laden", the prepositional phrase about the hunt for Osama bin Laden will receive the obl -i.e., noncore -dependency label (this is the annotation of such dependents of ASK in UD EN EWT ).
in the sentence "We asked the president whether Americans are safe at home", the subordinate interrogative clause, being an argument, is a core dependent, so it will be annotated as ccomp (again, this is the annotation of such subordinate clause dependents of ASK in UD EN EWT ).