The most common and most likely answer to this crossword clue is the 6 letter word SKILLS
I've seen this crossword clue in The Guardian
S
K
I
L
L
S
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 = skills.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 SKILLS mean?
SKILLS verb- To set apart; separate.
- To discern; have knowledge or understanding; to know how (to).
- To know; to understand.
- To have knowledge or comprehension; discern.
- To have personal or practical knowledge; be versed or practised; be expert or dextrous.
- To make a difference; signify; matter.
- To spend acquired points in exchange for skills.
- Capacity to do something well; technique, ability. Skills are usually acquired or learned, as opposed to abilities, which are often thought of as innate.
- Discrimination; judgment; propriety; reason; cause.
- Knowledge; understanding.
- Display of art; exercise of ability; contrivance; address.