The most common and most likely answer to this crossword clue is the 5 plus 5 plus 7 letter word GREAT TRAIN ROBBERY
I've seen this crossword clue in Financial Times
G
R
E
A
T
T
R
A
I
N
R
O
B
B
E
R
Y
Buddy explains!
The straight part
We know that "well-known job" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case well-known job = great train robbery.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.