What type of environmental scientist is likely to study the interactions of gorillas?
It depends on the type of interaction, but this typically wouldn't be an environmental scientist at all.
A primatologist, or a biological anthropologist, is most likely to study interactions among gorillas. Primatologists study primate behavior, ecology, intelligence, anatomy, and so forth.
A biologist or ecologist could also study gorillas and this wouldn't be unusual. They would likely study gorillas from a different perspective than a primatologist, who would be trained mainly in primates. A biologist would typically have a broader background that expands beyond primates.
Environmental scientists typically wouldn't study gorillas, although it's not impossible for someone to step outside of their field a bit.
Please note that these are all just generalizations. While most people studying gorillas come from a background in primatology, there are no steadfast rules determining who can study what.