Port? Jack has a Spanish wine (5)
I believe the answer is:
rioja
'spanish wine' is the definition.
(I've seen this before)
'port? jack has a' is the wordplay.
'port?' becomes 'rio' (I've seen this before).
'jack' becomes 'j' (playing card abbreviation).
'has' means one lot of letters go next to another.
'rio'+'j'+'a'='RIOJA'
(Other definitions for rioja that I've seen before include "Spanish wine type" , "Wine from northern Spain" , "wine region" , "Spanish wine variety" , "kind of red" .)