Answer:
The mssing punctuation of the text is the following:
<em>There was no drop in the author´s confidence when the film of his novel, which involved two years writing, was badly received by cinema audiences. The spokesperson for the studio defended the film´s release. It was an ambitious project. We’re very proud of it.</em>
Explanation:
In the fist sentence, there is a <u>possesive apostrophe missing</u> (author´s confidence).
In the first sentence, <u>commas should be place to separate the non restrictive subordinating clause</u> from the rest of the sentence. Non restrictive clauses are not esssential to the meaning of the sentence.
The second sentence starts with subject "The spokesperson" so <u>a period should be placed before the subject.</u> In this sentence we also should add a <u>possesive apostrophe</u>: film´s release.
The third sentence starts with the personal pronoun "it" acting as a subject so <u>a period should be placed before the subject</u>.
The last sentence is correctly punctuated.