What is the noun clause in the sentence: "We won't know whom the students chose for cheerleader until Monday morning."?
The noun clause is whom the students chose for cheerleader.
A noun clause can function as a subject or an object in a sentence.
To identify a noun clause, the questions What or Who (or Whom, if it is the object) can be asked of the verb.
In the given sentence, if we ask Whom of the verb know, we get whom the students chose for cheerleader.