Clue about questionable proof giving sign of creature's passing (9)
I believe the answer is:
hoofprint
'sign of creature's passing' is the definition.
'hoofprint' can be an answer for 'sign' (hoofprint is a kind of sign). I'm unsure of the 'of creature's passing' bit.
'clue about questionable proof' is the wordplay.
'clue' becomes 'hint' (synonyms).
'about' means one lot of letters goes inside another.
'questionable' indicates anagramming the letters.
'proof' with letters rearranged gives 'oofpr'.
'hint' going around 'oofpr' is 'HOOFPRINT'.
'giving' is the link.
Can you help me to learn more?
(Another definition for hoofprint that I've seen is " Mark left by rhino perhaps".)