One may care for canines barking in lengthiest day (6,9)

I believe the answer is:

dental hygienist

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'one may care for canines' is the definition.
I can't judge whether this defines the answer.

'barking in lengthiest day' is the wordplay.
'barking' is an anagram indicator ('barking' can informally mean mad).
'in'+'lengthiest'+'day'='inlengthiestday'
'inlengthiestday' with letters rearranged gives 'DENTAL HYGIENIST'.

Can you help me to learn more?

I've seen this clue in The Telegraph.

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