It's a question of location (5)
I believe the answer is:
where
I believe this is a double definition.
'it's a question' is the first definition.
(I've seen this before)
'location' is the second definition.
(thesaurus)
'of' is the link.
(Other definitions for where that I've seen before include "In which position?" , "a question of location" , "A question of place?" , "At which point" , "enquiry" .)