Final answer:
An investigator would conduct an experiment where a child observes liquid being transferred between different shaped containers, assessing the child's understanding of the concept of conservation as per Jean Piaget's developmental stages.
Step-by-step explanation:
An investigator who wishes to determine whether a child understands the concept of conservation would most likely perform an experiment that involves observing a child's reaction to the changes in the shape of a container while the quantity of its contents remains constant. This classic experiment might involve pouring the same amount of liquid from a short, fat glass into a tall, skinny glass and asking the child whether the amount of liquid is the same or has changed. The child's response would give insight into their level of cognitive development related to conservation, which is a concept developed by Jean Piaget, reflecting the understanding that certain properties of objects remain the same despite changes in their form or appearance.