我不知道我到底应该在什么情况下使用他 英文怎么说如题 谢绝翻译器 这么说对吗？I don’t know how can I use “jondatmal” in correct situation.

I don't know when I should use it.
用when指代何种情况就好。

I don't know under what circumstances I should use it.
这么说对吗？I don’t know how can I use “jondatmal” in correct situation.
不对。。。
你这样是说： 我不知道在正确的情况下，怎样使用。。。
意思不对。。。
应该：
I don't know under what circumstances I should use ”jondatmal“ .
或是
I don't know when I should use ”jondatmal“ .

I don't know when should I use it.
I don't know on what condition can I use it.

I don't know under what kind of condition/situation that I can use this.