The most common and most likely answer to this crossword clue is the 9 letter word WHEREUPON
W
H
E
R
E
U
P
O
N
More clues leading to the result WHEREUPON
Buddy explains!

The straight part
We know that "At which point" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case at which point = whereupon.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 WHEREUPON mean?
WHEREUPON conjunction- After which, in consequence.
- Upon which.