How can I see (and change) what sensitive notifications are? Android Help says:


  Control how notifications show on your lock screen
  
  [...]
  
  Option 4: Hide sensitive content from notifications on your lock screen
  
  
  Open your phone's Settings app.
  Tap App &amp; notifications and then Notifications. 
  Under "Lock screen," turn off Sensitive notifications.
  


However, I cannot find any information on what is actually considered a sensitive notification.

So, how can I see (and possibly change) what sensitive notifications are?
The notification's sensitivity (visibility) is set by the developer, but can be overridden (to some extent) by the user.

There are 3 types of notification's lock screen visibility:


Public: not sensitive, the full content is always shown on the lock screen
Secret: never shown on the lock screen
Private: sensitive, only the basic info (title and short content) is shown, but the full content is hidden


By default, all notifications are private (sensitive) unless overridden by the developer.

Changing the "On the lock screen" setting affects all notifications:


Don't show notifications at all: all notifications are treated as secret
Show all notification content: all notifications are treated as public
Hide sensitive notification content: all notifications are treated as private, except for public notifications.


The user can also control per-app notification visibility, either from the app itself or from the Android system (general setting on Android 7.1 and below, or more fine-grained using notification channels on Android 8.0 and above).

Though, based on self-experiment, it's impossible to override per-app notification visibility to higher visibility than the general lock screen's setting. (e.g. when the lock screen is set to "Don't show", setting per-app to "Hide sensitive notification" does not work and instead will not show any notifications).