Final answer:
The study will likely show activation in the mirror neuron system of the observer monkey, which are neurons enabling action recognition and imitation.
Step-by-step explanation:
The study involving an "observer" monkey watching a "demonstrator" monkey perform goal-directed movements is likely to find that neurons have been activated in the mirror neuron system of the observer monkey. These specialized neurons enable primates to recognize and imitate actions they observe being performed by other primates. The presence of these neurons suggests a mechanism for understanding and reproducing the actions of others, a fundamental component believed to be crucial for the development of language and complex social interactions.