The most common and most likely answer to this crossword clue is the 8 letter word WILDFOWL
I've seen this crossword clue in The Guardian
W
I
L
D
F
O
W
L
Buddy explains!

The straight part
We know that "Duck?/Duck?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case duck?/duck? = wildfowl.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 WILDFOWL mean?
WILDFOWL noun- Any wild bird such as ducks, geese or swans.
- Waterfowl.
- To hunt wildfowl.