日本銀行 is translated as "Bank of Japan".
(1) This would mean that it's a possessive, however no の is used. Is it omitted?
(2) Then, is it an appositive possessive, meaning 'Japan' identifies 'Bank'?
(3) Or is it one type of nominal apposition which does not have to use の anyway, which would mean that we could rephrase like this: 銀行は日本です.
2 and 3 would mean that "Bank Japan" would be the correct translation. We see it in "My friend John", and in German it is common, but I have been told by English speakers that it is uncommon to follow the "subject" with its name like this (University NewYork, Island Madagascar).
(4) Or is 日本 a noun adjunct, and it is not identifying the noun 銀行, it's not its name, therefore no appositive. Just like "Chicken soup", 日本銀行 would be a compound noun: "Japan-Bank" / "Japan Bank".