是I don't know what to do 吧？
作宾语，不是宾语从句，what to do就是个带疑问词的不定式短语，
不是句子，主语谓语都没有。
不定式作宾语有两种情况：一是及物动词后直接跟带to的不定式，二是“动词+疑问词 +带to的不定式”。
⑴“动词+带to的不定式”结构：常见的以不定式作宾语的动词有afford, agree, believe, decide, fail, hope, want, plan, choose, prepare, forget, remember, begin/start, learn, promise,refuse, wish等。如：
I can’t afford to buy a house.
⑵“动词+疑问代（副）词+不定式”结构：常见的这类动词有advise, decide, forget, know, learn, remember, see, tell, think, teach, wonder, understand, guess, explain等。这类疑问代（副）词what, when, which, where, how, whether等（不包含why）。如：
She does not know how to go there.
He will tell you when to start.
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