There are a few antennas being used (mainly the antenna cables near the charging port are used for cellular 3g/4g) and a few things you should check is if imei is displayed when dialing *#06#, also modem firmware and imei displayed in settings > general > about phone.
I would expect some board-level repairs needing to be done after liquid damage.
I recommend taking the phone to a reputable repair shop that does board-level / liquid damage repairs for liquid damage evaluation.