The most common and most likely answer to this crossword clue is the 8 letter word DOUBLE-U
I've seen this crossword clue in The Times
D
O
U
B
L
E
-
U
More clues leading to the result DOUBLE-U
Buddy explains!
The straight part
We know that "capital of Wisconsin/Blue duo" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case capital of wisconsin/blue duo = double-u.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 DOUBLE-U mean?
DOUBLE-U noun- The name of the Latin-script letter W.
- The WC; the toilet.