The most common and most likely answer to this crossword clue is the 4 plus 3 letter word KNOW ALL
I've seen this crossword clue in The Daily Telegraph
K
N
O
W
A
L
L
More clues leading to the result KNOW ALL
Buddy explains!
The straight part
We know that "wise guy" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case wise guy = know all.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 KNOW ALL mean?
KNOW ALL noun- Someone who obnoxiously claims to be knowledgeable on a subject.