The most common and most likely answer to this crossword clue is the 8 plus 2 plus 1 plus 4 letter word PORTRAIT OF A LADY
I've seen this crossword clue in The Times
P
O
R
T
R
A
I
T
O
F
A
L
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Y
More clues leading to the result PORTRAIT OF A LADY
Buddy explains!
The straight part
We know that "James’s version of the Mona Lisa" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case james’s version of the mona lisa = portrait of a lady.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.