I'd personally give the character a much broader scope of expertise than would happen in actual academia. This is a simple RPG thing to make his area of usefulness more broad. Since there's no other anthropologists in the group, doing this doesn't step on any toes.
An anthropologist is a specialist in human societies and how they interact. This overlaps with things like group psychology.
The usefulness of an anthropologist (the RPG version) is that he (or she) can predict, with reasonable accuracy, the actions of a group of people as well as identify their social structure in ways useful to players. In most cases (outside of the anthropologist's specialty) this information will be generic and pretty broad, yet still useful. A missed roll is likely that the information inconclusive ("it's a ... ritual item." "you always say that." "it's anthropology code for 'we have no idea what it does.'"). A fumbled roll means the anthrologist misinterprets information and draws the wrong conclusion.
The character likely has broad but shallow knowledge based on averages and examples from similar situations. The anthropologist has been trained to notice certain things that most people will not have been trained to notice. Like a Marine Scout might observe a desert town is note a certain building in the center of town is important and likely a place where they store food. The anthropologist will note the same thing but go on: "There's a single, central granary from which the entire town is fed, meaning they've collectivized their food production, but otherwise the society doesn't seem too oppressive. I'm guessing the area isn't very suited to agriculture, so food production and defense against hoarding is a thing. We might be able to get access to their leaders with an offering of that three tons of Ander's Red Corn we picked up..."
For instance, to mark the difference between Streetwise and Anthropology, the party is trying to find a kidnapped noble's child. They wander into the "bad" part of town.
* Both could identify the territory of a gang by markings, how people behave, and so on.
* Both could tell you its structure in broad terms.
* Both could tell you what a gang does for money (or if it is a kind of non-profit defensive collective).
* Both could tell you what is likely to trigger the gang to hostility.
* Both could tell you where their likely hangout is.
* Both could tell you what the relative rank of a gang member is and their responsibilities.
* Only Streetwise could tell you the ranks of the gang and how many ranks they have.
* Only Streetwise could tell you who the actual members are by name.
* Only Streetwise could tell you how to actually make peaceful contact.
* Only Streetwise could tell you where the actual hideout is.
* Anthropology could quickly draw up a sketch of what ranks gang members are in a gathering, and if there's a difference between the apparent rank of a gang member and his actual rank by observation. Streetwise could do similar, but to get exact information someone with Streetwise could approach people and talk to them without standing out. This might tip the gang off ('someone's been asking questions').
* Anthropology could estimate the likely size (in members or controlled territory), activities, and what the gangsters value based on cursory, incomplete information.
* Anthropology could derive other statistics about the greater society by simply observing the gang. ("It'd seem that the world has a prejudice against that group", "Given that broadbase membership, it's likely the world is pretty egalitarian and these are just the unlucky who fell between the cracks.", "Gonna bet there's probably been a civil war on-world of some sort or maybe they're refugees from a world like that ... yeah, you can tell from the membership and how they treat others, in a generation or two they'll probably go into more standard organized crime stuff unless the local government ca...er nevermind.")
In this way, for instance, an anthropologist and someone with Streetwise can actually work together to an end without necessarily stepping on each others toes that much.
For instance, an anthropologist will come across an artifact: A cross-shaped lash-up of wood. There's an old Imperial Marine helmet at the top of the cross, then there's lengths of leather cord from which things are hung on the crossbar. The wooden lash-up is planted in a cairn of stones. There's any number of interpretations to this, some of which players might not know. A roll by the anthropologist (along with any information he or she has to gleaned from the culture in question to put it into context) would inform the players:
* It is a cairn burial of a Marine from the locals whom the locals considered one of their own. ("notice there are offerings of common meat and alcohol but a lack of money or jewelry. This is likely a burial site, with offerings for the departed of the things he enjoyed in life.") Dealing with them will be easier, because they're likely to know what the Imperium is.
* It is a symbolic altar of a god or spirit, whom the locals apparently treat as a kind of intercessory figure. ("notice there are votive statues at the base, the offerings are more symbolic than practical, and the sacrifice of high-value or value-added objects like woven shellfish shell necklaces. It's likely the locals consider off-worlders as gods or spirits.") Dealing with them will be difficult as they are likely to be supersitious, and denials of their divine status may threaten their worldview and lead to 'defensive' violence.
* It is a boundary marker and a sign of strength. ("the helmet's been ritually disfigured, likely to 'neuter' the power of the Marines.") Again, the natives are likely to at least be wary of off-worlders, likely hostile.
* It is a boundary marker and a sign of allegiance. ("the helmet's been decorated with ribbons and there's necklaces with the Imperial sunburst on it.") The natives are likely to believe themselves in fealty to the Imperium and likely to have had friendly contact. They're advertising to the other locals that they're not to be messed with because they're allied with the Imperium.
While dealing with "primitive" cultures might seem to be the common realm of such scientists this kind of knowledge of human relationships, the basic human relationships that anthropologists study are pretty much universal. (Okay, snooty academic time: "sociologists" of course study "advanced" cultures such as your own or ones you'd consider your peers, but we can just roll this in.) "You'll notice the dominance/submission rituals are pretty similar across human cultures be it in the megacorporate boardroom, the Imperial Marines, or in those kelp-gliders on Mantana III."
It's also important to remember that since humans have encountered non-human cultures, those aliens have given us invaluable insights into the nature of humans which are only possible from totally unrelated outsiders: So I think interpreting signals would not be as difficult as a GM might assume, since the academic has access to centuries of observations of human behavior made by Aslan, Vargr, and Hivers.
