Research for existing websites

I am new to the UX research field and I'm looking for insight on how to conduct research on products that already exist, (in this case, websites). My boss is asking me to find out very specific information in the vein of, "We need to know what the needs are related to ____ area of the site" which I'm having a difficult time grasping. I think my confusion is coming from not being sure how to do research when you have such a narrow area of focus. What if people aren't even using the site or using it in the way we expect?

What research method would be best suited for finding out this kind of information?