Clauses help!

Everyone knew why we concluded very specific data in the report.

Is this a Noun Clause as an object.
Or a as a Predicate Nominative?

I believe that “why we concluded very specific data in the report” is a noun clause, the object of “knew.” As you know, a noun clause is often a substitute for the word “something”: Everyone knew something. Furthermore, “knew” is not a linking verb, so the clause cannot be a predicate nominative.

What is the Predicate nominative anyway, can you explain more?

Some people do not like the term “predicate nominative.” They prefer “subjective complement” or “predicate noun.” No matter what you call it, I believe that it refers to the word(s) that comes after a linking verb and that refers to the subject: “Englishtest” is an English helpline. As you can see, “An English helpline” comes after the linking verb “is” (which is something like an = symbol) and refers to the subject “Englishtest.” That is: Englishtest = an English helpline. If you say “Mona is beautiful,” then we call that kind of subjective complement an predicate adjective, if you wish to; In the “Teacher is he/him,” you may call that subjective complement a predicate pronoun, if you wish. One of my favorite grammar books gives this example of a noun clause being used as a predicate nominative: The question is whether he can be nominated. As you can see, this means: The question = whether he can be nominated.