The most common and most likely answer to this crossword clue is the 4 letter word POOH
I've seen this crossword clue in The Times
P
O
O
H
More clues leading to the result POOH
- Upset, small twin rings and knocks
- Pompous official in Bear Inn in conversation
- Spinning basket for bear
- Bear an expression of disgust
- Bear band’s return
- Bear has something to go through backwards
- Bear with oddly brash, pompous official
- Bear ridicule, when it’s repeated
- Repeatedly ring up and scornfully dismiss
- Character who made ‘The More It Snows’ ring round
Buddy explains!

The straight part
We know that "knocks" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case knocks = pooh.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 POOH mean?
POOH noun- Feces.
- A piece of feces or an act of defecation.
- Cannabis resin.
- Champagne.
- To defecate.
- To dirty something with feces.
- Expressing annoyance, frustration, etc.: a minced oath for 'shit'.
- Short for shampoo.
- An instance of saying "pooh".
- To say "pooh".
- To say "pooh" to.
- Expressing dismissal, contempt, impatience, etc.
- Expressing disgust at an unpleasant smell.