Question

What happened to him? I don’t know_________________（宾语从句）

Answer 1

I　don＇t　know　what　happened　to　him。　或者
I　don＇t　know　what　has　happened　to　him．
变成宾语从句要用陈述句词序和注意时态，但what　happened　to　him本身就是陈述句词序：what主语　happened谓语　to　him（介词宾语）。
因主句I　don＇t　know是现在时，　所以从句中可以用各种时态，　即原来用的过去时态不必改变。
就是what happened to sb和what's wrong with sb无论是问句还是宾语从句中都保持一个语序，　因为在这两个句子中what都是主语。

Answer 2

你好:
I don't know ( what is wrong with him ) ?

what happened to him = what is wrong with him.

翻译: 我不知道他怎么了.

希望对您有帮助!

追问

也就是what happened to sb和what's wrong with sb无论是问句还是宾语从句中都保持一个语序是么？

追答

你好:
楼主, 这里的 I don't know 是插入语 , 可以省略的, 所以才能用 what is wrong with him.

如果是陈诉句里的疑问语气, 那都要用陈诉语序 如: He asked me what my father's job is ?

追问

我是想问what's wrong with him 和what happened to him无论是宾语从句还是问句语序是否一样

追答

你好:
是一样的......

Answer 3

I don't know what happened. 我不知道发生了什么。