Human personality is related to emotion, still an annoying mystery.
However, fewer than ten easily described personality traits (novelty seeking/avoidance, conservatism, affect, emotional range, etc) may need to be measured.
The most important element is intelligence, specifically the type of
intelligence. This depends on what problems someone most wants to deal with (in my case, finishing all my projects before celebrating forever).
The subject could describe their ideal life and ideal environment.
Since we don't know what matters yet, there may be millions of mini-quizzes and measurable factors. Later, there will be fewer but far more incisive personality tests.
These may be surreal trips through ultra-resolution VR-space, and involve being
exposed to thousands of images per minute.