The most common and most likely answer to this crossword clue is the 5 plus 5 plus 6 letter word ABOUT ONE’S PERSON
I've seen this crossword clue in Financial Times
A
B
O
U
T
O
N
E
â
€
™
S
P
E
R
S
O
N
More clues leading to the result ABOUT ONE’S PERSON
Buddy explains!
The straight part
We know that "on one" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case on one = about one’s person.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.