(1) I don't know what graph theory is.
According to the grammar, I believe it should be:
(2) I don't know what is graph theory.
But is it spoken colloquially the way I wrote it in (1)?
We don't find subject-auxiliary inversion if the wh-word is the subject:
- Who killed Cock Robin?
- Who is coming to dinner?
We could assume the same is true for:
- What is graph theory?
So it seems that we might assume that the embedded questions look like this:
I don't know who killed Cock Robin.
I don't know who is coming to dinner.
I don't know what is graph theory.