Answer:
Subject
Explanation:
A noun clause is a group of words with a subject and a verb whose function is to acts as a noun in a sentence, thus, it can be a subject, a direct or indirect object, a predicate nominative, or an object of a preposition. We can identify them because they tend to begin with the words how, that, what, whatever, when, where, whether, which, whichever, who, whoever, whom, whomever, or why.
In the sentence given, the noun clause “what she should do next” is acting as a subject because it is the thing being discussed and dealt with.
