The most common and most likely answer to this crossword clue is the 8 letter word SKI-BOBS
I've seen this crossword clue in The Guardian
S
K
I
-
B
O
B
S
Buddy explains!
The straight part
We know that "goes dow/nhil/l" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case goes dow/nhil/l = ski-bobs.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.