The most common and most likely answer to this crossword clue is the 8 letter word KNOW-HOW
I've seen this crossword clue in The Times
K
N
O
W
-
H
O
W
More clues leading to the result KNOW-HOW
Buddy explains!

The straight part
We know that "Expertise" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case expertise = know-how.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.
What does KNOW-HOW mean?
KNOW-HOW noun- The knowledge and skill to be able to (do something correctly).