The most common and most likely answer to this crossword clue is the 10 letter word PEDANTRIES
I've seen this crossword clue in The Guardian
P
E
D
A
N
T
R
I
E
S
Buddy explains!

The straight part
We know that "Nit-pickings" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case nit-pickings = pedantries.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 PEDANTRIES mean?
PEDANTRIES noun- An excessive attention to detail or rules.
- An overly ambitious display of learning.