My single bit of trivia: the knob on a deer's antler is a crown (7)
I believe the answer is:
coronet
'a crown' is the definition.
(coronet is a kind of crown)
'my single bit of trivia' is the wordplay.
'my' becomes 'cor' (both are expressions of surprise).
'single' becomes 'one' (synonyms).
'bit of' indicates taking the first letters.
The initial letter of 'trivia' is 't'.
'cor'+'one'+'t'='CORONET'
'the knob on a deer's antler is' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
(Other definitions for coronet that I've seen before include "topping item of jewellery" , "badge of rank" , "Peer's headgear" , "jewelled headdress" , "Not genuine" .)