Use a photoresistor to read an IR LED from an Itron energy meter
I want to know if it is theoretically possible to use a normal photoresistor to read this values.


Theoretically, yes.


  If yes, how can I specify the photoresistor?


By choosing one that is sensitive to the IR wavelength range. Which most common ones are not. As seen in this datasheet, photoresistors tend to peak at 650nm, right in the middle of the visible light range.


  If not, what would be the alternative?


So you need something that is sensitive to the IR wavelength range. 900 - 1300nm is typical. What you want is a IR Phototransistor.