There's a couple of points to make here.Hello,
Suppose this dialogue happens, B tries to understand the resource of the data. is b's question correct ? or how do you ask instead?
A:it's either p1 or p2
B:according to which one is that true?
Over your example,I want to detail itIt's sounds very strange to begin a question with 'according to'. It can be followed by either a person or some other source of information:
According to you, the answer is X. (= you said X)
According to this book, the answer is Y. (= this book says Y)
But I don't think you can ask about who said it, or about which book says it, using 'according to':
According to who is the answer X?
According to which book is the answer Y?
(The book is the source of this information, on this occasion. It's a resource if it contains lots of information that you could use from time to time.)