Some dialogue Jack pens right for old script (6,1)
I believe the answer is:
linear b
'old script' is the definition.
(ancient writing)
'some dialogue jack pens right' is the wordplay.
'some dialogue' becomes 'line' (as in an actor's lines).
'jack' becomes 'ab' (both can mean a sailor).
'pens' is an insertion indicator (to pen can mean to contain or imprison).
'right' becomes 'r' (common abbreviation).
'ab' enclosing 'r' is 'arb'.
'line'+'arb'='LINEAR B'
'for' acts as a link.
(Other definitions for linear b that I've seen before include "Ancient writing used at Knossos" , "Early signs" , "Old script" , "Ancient Minoan script" .)