How do you read internal temperature on the PIC18F?
The temperature diode is internally connected to the ADC. There is no pin access. ADC setting of CHS = 0b11100 simply selects the temperature diode as the ADC channel. The connection is internal. The idea is that the ADC is used to make the conversion on the internal diode as the input. The result will change over temperature.
Please read Application Note AN1333, which discusses about calibrating this temperature indicator. This note refers to PIC12 and PIC16, but can be extended to PIC18 as well.