He asked his mother where it happened 和He asked his mother how it happened到底那个句子正确

He asked his mother where it happened 和He asked his mother how it happened到底那个句子正确

都正确.
第一句是：他问他的妈妈事情是在哪里发生的.
第二句是：他问他的妈妈事情是如何发生的.

两个都对

都正确，where it happened和how it happened都是正确语序的宾语从句

都对，意思不同。