There is no one place in the library to find ethnographies. There are many books in the library that are ethnographies, and other ethnographic studies will be found in journal articles. Take a look at the categories below to find ethnographies in different formats. If you're looking for names of indigenous peoples, check out Wikipedia's list of indigenous peoples.
To find books that are or include ethnographies, search the online catalog. Instead of searching for "Ethnography", try "Ethnology" as part of a subject search. For even better results, pair "Ethnology" with a particular region or country. Two other subject searched that work well are "Indigenous Peoples" and "Ethnic Groups". It is also best to pair them with a region or country.
You might have even better luck using the name of the individual ethnic group as your search terms. Keep in mind, however, that common names for ethnic groups may vary or not be the same as the official subject terms. For example, the subject heading for the Ibo is "Igbo (African people)". Fortunately you'll see clues while you search.
Another trick is to try doing an advanced search combining a geographical or group name on one line and "ethnograph?" on another line. The ? at the end of ethnograph- allows you to search for ethnography, ethnographies, and ethnographic all at the same time.
If there is a particular aspect of a group's culture you are interested in, start with that specific term (ex: Folk music, ethnopsychology, etc). Combine that term with the geographic name or name of the group of people.
In the library, many ethnographies are in the GNs. where much of the anthropology collection is found, but others will be in D (world history) or E and F (History of the Americas). Ethnomusicology will be found in M.