彼が昨日誰を見たのか私は知らない。(Correct) I don't know whom he saw yesterday. 彼が昨日本を何冊読んだのか私は知らない。(Correct) I don't know how many books he read yesterday. 彼が昨日ど[れ]の本を読みたかったのか私は知らない。("れ" is not needed) I don't know which book he wanted to read yesterday. 彼が昨日読んだ本の[タイトル or 題名]を私は知らない。("題" is grammatically correct, but it's more like a written Japanese.) I don't know the title of the book that he read yesterday. Actually you don't have to say "私は", unless you want to emphasize that these sentences are about yourself. Hope it is helpful.