Grammar 
Noun Clauses - NC being used as the direct object
日本語で --> 間接疑問文(かんせつぎもんぶん) in the following sentence pattern S + V + 疑問詞 + S + V
NOTE: In most of the textbooks, this particular grammar point is found around the Relative Pronouns and/or Relative Clause section of the textbook, which is why this grammar point was confusing to disect. I have been looking at this grammar point from a 'relative' standpoint, instead of a 'noun clause' standpoint. This particular grammar point I would define as a 'mathlish'. Meaning, the way Japanese grammar books define this pattern (S + V + 疑問詞 + S + V) looks more like a math problem than anything pertaining to the English language. Furthermore, the textbook writers took this 'mathlish' grammar point and made it even more confusing. They only want to study noun clauses used as direct objects when the clause is preceded with a subject and verb. The way this whole grammar point has been approached, leaves me in wanting to follow in the Japanese footsteps and create my own 'wasei-eigo' word: Jamamarlish (Japanese + math + grammar + English).
Definition: In more simple terms, this particular grammar point focuses on noun clauses. A noun clause is a clause which does the work of a noun in the sentence. These clauses must contain a subject and verb. Look at the sentences in the table below for clarification. Noun clauses begin with the following words: that, what, where, when, who, whom, which, whose, how, why, whether, etc.
Noun clauses can be used in various forms (subject of a verb, direct object, complement, etc.), but you don't have to worry about these various forms because the textbooks only to focus on the noun clause when it's being used as a direct object. More specifically, noun clauses that are preceded by a subject and verb. Look at the mathlish formula above for clarification.
One last thing to note about Noun clauses being used as direct objects is that they sometimes look like relative clauses. Take for example the following sentences:
Before you stress out about not being able to distinguish between these two types of sentences, RELAX!! It's easy to distinguish them! Relative clauses can ALWAYS be replaced by which and/or who and the sentence still makes sense. This cannot be said for noun clauses.
| Example Sentences: |
New Horizon | I do not know what you mean. s v starter of noun clause noun clause |
One World | I can't tell where my house was. s v starter of noun clause noun clause |
Example Sentences: |
Sunshine | I know how you feel. s v starter of noun clause noun clause |
Total English | I know why Jim didn't come. s v starter of noun clause noun clause |
More example sentences
Fun Fact: "All pilots on international flights identify themselves in English." (source)