In Fellow, there are several different types of streams with different visibility.
You'll be able to tell the type of stream (and the related visibility) by looking at the icons by the stream name. This is the general structure:
Types of Streams
Meetings: Only visible to meeting attendees
1-on-1s: These are only visible to the two people involved
Private: Visible only to you
Shared: Visible to whoever it has been shared with
Public Links: Visible to anyone with a link
See who has access to the stream
By clicking on the blue Share button, you can see the names of the people who have access to the stream.
You can also click on the avatars in the note to see who is shared on each note!
But for public links, you won't be able to identify who is watching the note. Instead these people will appear as Anonymous.