what is the readout pin of those sketches? about arduino-dsmr HOT 1 CLOSED

That depends. You configure this library by passing a Serial object (specifically, any Stream instance) to it, from which it will read data. In the read.ino example, there is:

P1Reader reader(&Serial1, 2);

Which sets up the library to read from Serial1, which is available on e.g. an Arduino Mega. What the RX pin is that corresponds to this serial port depends on the Arduino board you're using, see the docs for the board for more info.

Also note that not all boards (e.g. a Uno) have multiple hardware serial ports, which means you either have to use SoftwareSerial (or similar such as AltSoftSerial) to emulate a second serial port, or use the primary serial port (but then you cannot use the serial port for debugging, if you also open up the serial monitor, you'll create a conflict on the primary serial port).

from arduino-dsmr.