。
The question is who will make the decision.
Literal
Problem [topic-は] who [subj-が] decision [obj-を] hand-down [embedded-Q-か] [という thing-だ].
決定を下す ('hand down a decision, render a decision') is a formal collocation — 下す ('lower, bring down, render') used for authoritative decisions. Similar collocations: 判決を下す ('render a verdict'), 命令を下す ('issue an order').