。
The question is who will bell the cat.
Literal
Problem [topic-は] who [subj-が] cat [on-に] bell [obj-を] attach [embedded-Q-か] [copula-だ].
A reference to Aesop's fable 'Belling the Cat,' where mice agree to put a bell on a cat to warn them of its approach but no one volunteers to do it. The phrase 'to bell the cat' means to take on a dangerous task for the group's benefit. Faithfully translated into Japanese.