It's a noun in the expression "to have one's say". For example, The Queen has had her say. A learner may want to be able to recognize this expression but shouldn't try to use it.In your original sentences, you seem to have tried to use "say" as a noun. It's not. It's a verb.
"Let's see what will Her Majesty's say be."
"Let's see what will be Her Majesty's say."
Which form is more correct? Thank you
I've been finding "say" as a noun long since in colloquial English, and in the newspapers. "Such was the case with the Queen's say, about the recent announcement of Prince Harry's appointment to Captain General, Royal Marines. An appointment Prince Philip is going to stand down from." Further, I've been studying English for over 65 years; I still consider myself a learner, but I can't see why I couldn't use the expression if it does make sense in English. If this worries you, let's replace "say" with "decision". My question remains.
They are both unnatural. Here's another natural (but very formal) variation I just thought of: "Let's await Her Majesty's decision."But, just in case I would sound unnatural, which sentence could I be using:
"Let's wait what will be Her Majesty's decision", or
"Let's wait what H.M.'s decision will be"?
Furthermore, neither of them is less unnatural or more acceptable than the other. They are both simply wrong.Neither of your two sentences (Let's see what will Her Majesty's say be. Let's see what will be Her Majesty's say.) is acceptable/natural/grammatical in any atmosphere.