Question

She think lily is doing her homework,怎么辨宾语从句？

Answer 1

用一个句子充当宾语，叫做宾语从句。

She thinks 主句

Lily is doing her homework.从句作think 的宾语

Answer 2

从Lily开始到结尾，是省略了引导词that的宾语从句。另外，think应该是thinks。
通常宾语在谓语动词后面，只要是及物动词，或者动词后面是名词，就基本上是宾语。