The most common and most likely answer to this crossword clue is the 6 letter word LOQUAT
I've seen this crossword clue in Financial Times
L
O
Q
U
A
T
Buddy explains!

The straight part
We know that "How is the Japanese medlar also known" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case how is the japanese medlar also known = loquat.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 LOQUAT mean?
LOQUAT noun- The Eriobotrya japonica tree.
- The fruit of this tree. It is as large as a small plum, but grows in clusters, and contains four or five large seeds.