你能找出是谁杀了他吗?

宾语从句就是说从句是用来修饰宾语的
翻译时先把原话改成陈述句
你能找出是A杀了他，翻译为you can find out that A killed him
其中that就是宾语，A killed him就是修饰它的从句。
改成疑问句就好了，翻译为Can you find out that who killed him?
其中that因为不充当句子的任何成分，只是一个形式宾语，可以省略。
Can you find out who killed him?

翻译简单可惜我不知道啥叫宾语从句 － －
Can you find out who killed him?
Can you find out he was killed by whom?

Can you find out the person who killed him?

Can you find out who killed him?