The LPCOMP.PSEL register is used to select an analog input pin for LPCOMP. The pins available are AIN0 through AIN7.
See GPIO — General purpose input/output for more information about the pins. Similarly, you can use EXTREFSEL to select one of the analog reference input pins, AIN0 and AIN1, as input for AREF if it is selected in EXTREFSEL. The selected analog pins are acquired by LPCOMP when it is enabled through ENABLE.