Knock response, whether so disposed (4,5)

I believe the answer is:

whos there

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'knock response' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'whether so disposed' is the wordplay.
'disposed' is an anagram indicator.
'whether'+'so'='whetherso'
'whetherso' anagrammed gives 'WHOS THERE'.

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I've seen this clue in the Sydney Morning Herald.

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