“Can a person access the nāmagotta of someone else? For example, see the past lives of another person or even see past events of another’s current life?”
– Yes. Those with paracittavijānana ñāṇa have access to other people’s nāmagotta. For example, Buddha Gotama (our Buddha) was able to describe the life stories of many previous Buddhas.
“What happens to the nāmagotta of an arahant after parinibbāna?”
– They remain in the “vinnana plane” forever. Those are just records.
– That is why Buddha Gotama was able to read the nāmagotta of previous Buddhas.