Not documented, Pokemon Go now asks for Notification permissions. (Which is typical of mobile games and should have been done at launch, but ironic given current circumstances.)
Generally speaking, this is the worst way to do it, as the app hasn't made a case for why it needs to send notifications.
It should do it in a contextual way so the user understands that notifications will enhance their experience of the app.
This is what developers would do in the past with location access also, but as privacy awareness takes hold people are far more likely just to deny these permissions.
In iOS it's a pain for a user to actually reenable the setting after the fact.