Proof of ownership? Doctor deleted it (5,4)
I believe the answer is:
title deed
'proof of ownership?' is the definition.
(legal document which might show proof of ownership)
'doctor deleted it' is the wordplay.
'doctor' is an anagram indicator.
'deleted'+'it'='deletedit'
'deletedit' with letters rearranged gives 'TITLE-DEED'.
(Other definitions for title deed that I've seen before include "Document proving ownership" , "Document establishing legal right to property" , "proper document" , "Document giving legal right of ownership" , "Deleted it (anag.)" .)