Noun for person being observed

Wiktionary cites observee:, but it appears to be used mainly in scientific contexts:

Noun (plural observees)

• One who is observed.

Ngram: "observee"

• I do not know the student whom I came to observe, at this point the teacher will assist me by laying her hand casually on the observee's shoulder as she ends her.... From Ready-to-Use Information & Materials for Assessing Specific Learning Disabilitis

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• Thus, on days and at times selected by the observee, two observers show up at the observee' s work site and use a standard behavioral checklist to conduct a systematic 30-minute observation session, followed by interactive feedback... From Safety, Health, and Asset Protection

Subject. Wiktionary says

A human, animal or an inanimate object that is being examined, treated, analysed, etc