The most common and most likely answer to this crossword clue is the 7 letter word PINKING
I've seen this crossword clue in The Times
P
I
N
K
I
N
G
Buddy explains!
The straight part
We know that "Knocking" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case knocking = pinking.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 PINKING mean?
PINKING verb- To decorate a piece of clothing or fabric by adding holes or by scalloping the fringe.
- To prick with a sword.
- To wound by irony, criticism, or ridicule.
- To choose; to cull; to pick out.
- To become pink in color, to redden.
- To turn (something) pink.
- To turn (a topaz or other gemstone) pink by the application of heat.
- Of a motor car, to emit a high "pinking" noise, usually as a result of ill-set ignition timing for the fuel used (in a spark ignition engine).
- Of a musical instrument, to sound a very high-pitched, short note.
- To wink; to blink.
- Decoration by adding holes or scalloping.