observee

Observer and observee would probably want to get together prior to the lesson to discuss which aspects of presence should be tackled.

P is for Presence « An A-Z of ELT 2010

It seems to me that one of the advantages of the drones is that they are capable of observing from enough of a distance that the observee is unaware, thus maintaining surprise if a decision to strike is made.

WSJ: Militants used $26 software to hack U.S. drones 2009

I will write to my Lord in a few days, and when I hope to have seen the Dean, but from what his neighbour Mr. Woodcock told me yesterday, I shall have nothing very comfortable to tell him touchant la sante de son bon precepteur, ni sur la mienne; elle exige un management et une regime que je n'ai pas encore observee avec la rigueur necessaire.

George Selwyn: His Letters and His Life Helen [Editor] Clergue

I will write to my Lord in a few days, and when I hope to have seen the Dean, but from what his neighbour Mr. Woodcock told me yesterday, I shall have nothing very comfortable to tell him touchant la sante de son bon precepteur, ni sur la mienne; elle exige un management et une regime que je n'ai pas encore observee avec la rigueur necessaire.

George Selwyn His Letters and His Life Ed 1899

'Man! but ye made a rare lot of noise in here, 'observee Archie, thoughtfully.

The Nigger of the Narcissus 1897

Note that you don't even need to unregister your observer; it's handled for you when the observee is released.

andymatuschak.org 2009

[observee removeObserver: self forKeyPath: @ "someValue"];

andymatuschak.org 2009

* (* "Il eut pense commettre un sacrilege en gardant a son bord cette plaque respectee pendant pres de deux siecles par la nature et par les hommes qui pouvoient avant nous l'avoir observee."

Terre Napoleón; a History of French Explorations and Projects in Australia Ernest Scott 1903