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Q. How to identify the noun clause?

A noun clause has a subject and verb. It functions as a noun in a sentence.

For instance,

In the sentence, 'The Oliver Twist is written by Charles Dickens ,' The Oliver Twist is the name of a book and thus considered to be a noun. However, if the sentence would have been ' The book I was reading last night is written by Charles Dickens ' then the entire underlined part would be a noun clause which would act as a noun.

Thus, if the clause is acting as the noun, i.e. the thing that is being talked about, then it will be identified as noun clause.