If there is anyone out there who still doubts that America is a place where all things are possible, who still wonders if the dream of our founders is alive in our time, who still questions the power of our democracy, tonight is your answer.
本句的主句谓语是is，主句为tonight is your answer。主句前的是一个if引号的条件状语从句，is为谓语。who still doubts that America is a place where all things are possible, who still wonders if the dream of our founders is alive in our time, who still questions the power of our democracy，为三个修饰先行词anyone的定语从句，第一个从句里又有that America is a place where all things are possible做宾语从句，这里面的where all things are possible是修饰place的定语从句；第二个从句里又有 if the dream of our founders is alive in our time做条件状语。
译：如果现在依然有人怀疑美国是不是任何事情都可能发生的地方，依然有人疑惑我们国家的缔造者们的梦想是否还鲜活地存在于这个时代，依然有人质疑我们民主的力量，那么今夜你将得到答案。
资料：《不就是语法和长难句吗》——刘晓燕