英语语法: “to do” 是宾语或宾补
Source: Zhihu
(prepared by: alexcwlin; edited by: Adam Lam)

Question:
What I want to do. 其中不定式to do 是做宾语还是宾补，做宾补的话谁是第一个宾?

alexcwlin comments:
The infinitive “to do” here in this sentence is neither an Object 宾语nor an Object Complement宾补.

It is an Adverbial Phrase 副词片语which modifies the Verb “want” by stating “to do” is what the “want” is all about.

Notice that “what I want to do” is not a complete sentence. It is a Noun Clause which functions as the Subject of the sentence.

Let’s complete the sentence with a few added words like: “What I want to do is to go to a movie”.

“What” here is a Pronoun, which is the same as “that which”.

Substituting “that which” for “what”, the Noun Phrase becomes “That which I want to do”. “That” is a Pronoun being modified by the Adjectival Clause “which I want to do”.

For more on Noun Clause starting with “what”, check out:  https://grammar.yourdictionary.com/parts-of-speech/nouns/noun-clause.html