In indirect questions, the so-called penthouse principle disallows Subject-AV inversion.
Cathy wonders what did Sam eat. (Incorrect)
Cathy wonders what Sam ate. (Correct)
What is the rule for a sentence like this?
Might I know who that person is?
Might I know who is that person? (Incorrect)
The above sentence admits of inversion. I can see it has an embedded interrogative clause within the matrix clause (the whole sentence).
Why is there no inversion in the matrix clause but inversion in the embedded clause?