In ESP-12E NodeMCU, what's the pin number of A0?
The numeric value of A0 is 17, as defined here.

But unlike on an Arduino board, you can't use it as a digital pin. It only work for pin numbers 0-16.

If you are using as a parameter for analogRead, the numeric values would be 0 and 17, as seen here.

And as such, these three calls would do the same:

analogRead(A0);
analogRead(17);
analogRead(0);