The most common and most likely answer to this crossword clue is the 4 plus 4 plus 1 plus 4 letter word KNOW WHAT I MEAN
I've seen this crossword clue in Independent
K
N
O
W
W
H
A
T
I
M
E
A
N
Buddy explains!
The straight part
We know that "nudge, nudge (insinuation)" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case nudge, nudge (insinuation) = know what i mean.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.