Finally a question I’m well equipped to answer! There were a few kingdoms in South Nigeria that existed up through the 19th century before colonization so for this let’s use the Kingdom of Benin as this example.

Founded in the 10th century, the Kingdom of Benin existed until the late 19th century when it was annexed by British colonial forces. The kingdom was incredibly wealthy, with one of their main sources of economic income being through slavery and the trade of slaves (Igbafe 409) until the abolition of the slave trade in 1815. After this the kingdom specialized in agricultural trade with the British (Obinyan 34). That aside, the Benin Kingdom had contact with Europeans centuries prior to this, as in the late 15th century the Portuguese had contacted the kingdom (Osadolor 403). In fact, the Oba at the time even sent an ambassador, Ohen-Okun of Ughoton to Lisbon in order to “... to see more of both the people and the land” (Aisien and Oriakhi 110).

Many Europeans took a great interest in the kingdom, both in terms of trade but also as a site for Christian missionaries (although they were relatively unsuccessful), with contact lasting between the two powers for around four centuries. As such, despite having never left the kingdom you would likely be familiar with the existence of the British and other European powers. Doubly so due to the influence the Oba of Benin had in the 19th century, who imposed trade dues and embargos on the British, which was seen as frustrating by the British (Igbafe 386). In reaction to this, the British compelled the Oba to sign a treaty accepting British input on his governmental practices, external relations, and “‘the development of the resources of the country’” (Igbafe 387) as well as other agreements that would further open the kingdom to the British. However, despite this the Oba still continued to impose his trade embargos, which further frustrated the British. With all of this taken into account, you would know a fairly good amount about the external world, in particular European powers.

In terms of living conditions, the kingdom was described relatively positively (besides for the intentional negative statements by the British in the late 19th century). The kingdom is described as “...one of the most stable and centralized states in West Africa…” (Obinyan 30). However, due to British colonial aspirations, later writings on the Benin Kingdom intentionally painted the kingdom in a negative light via scientific racism. From then onward the “...Benin civilization was represented by writers as the crudest manifestation of inhumanity” (Obinyan 35). As such, I believe the best way to gauge the living conditions is to look at earlier writings. For instance a Portuguese captain wrote that Great Benin, where the Oba resides was “...wealthy and industrious. It is so well governed that theft is unknown and the people live in such security that they have no doors to their houses” (Elias 12) in 1691. Another great source for this is from the Dutch writer Olfert Dapper in his writing titled Naukeurige beschrijvinge der Afrikaensche gewesten, or Description of Africa. This was written in the late 17th century and describes the royal palace for the Oba, containing “...many magnificent palaces, houses and apartments of the courtiers…” (Dapper) and “All of them are being very well maintained”. From this we can somewhat assume that living conditions were relatively well in the Kingdom of Benin, up until British colonization.

Citations

Igbafe, Philip A. “Slavery and Emancipation in Benin, 1897-1945.” The Journal of African History, vol. 16, no. 3, 1975, pp. 409–429. JSTOR, www.jstor.org/stable/180474. Accessed 28 Apr. 2021.

Aisien, Ebiuwa, and Felix Oriakhi. “Great Benin On The World Stage: Re-Assessing Portugal-Benin Diplomacy In The 15th And 16th Centuries.” IOSR Journal of Humanities and Social Science, vol. 11, no. 1, 2013, pp. 107–15. IOSR Journals, doi:10.9790/0837-111107115.

Osadolor, Osarhieme Benson, and Leo Enahoro Otoide. “The Benin Kingdom in British Imperial Historiography.” History in Africa, vol. 35, 2008, pp. 401–418. JSTOR, www.jstor.org/stable/25483729. Accessed 28 Apr. 2021.

Igbafe, Philip A. “The Fall of Benin: A Reassessment.” The Journal of African History, vol. 11, no. 3, 1970, pp. 385–400. JSTOR, www.jstor.org/stable/180345. Accessed 28 Apr. 2021.

Obinyan, Thomas Uwadiale. “The Annexation of Benin.” Journal of Black Studies, vol. 19, no. 1, 1988, pp. 29–40. JSTOR, www.jstor.org/stable/2784423. Accessed 28 Apr. 2021.

Elias, T.. "Africa and the development of international law." Boston, Springer Netherlands, 1988.

Dapper, Olfert. "Naukeurige Beschrijvinge Der Afrikaensche Gewesten" Houten-Netherlands, Netherlands, Bohn Stafleu van Loghum, 1668, archive.org/details/gri_33125009359999.

In the mid-19th Century, living in coastal Nigeria--say in Lagos around 1861 or so-- a man with elite status likely knows a fair amount about the rest of Atlantic West Africa and about the states and societies to his north, as far as the recently-formed Sokoto Caliphate. He may have direct financial ties to other centers of Atlantic trade further up or down the coast--Ouidah, Anomabu, Calabar, etc.

He certainly knows a fair amount about the United Kingdom because in 1861 Lagos was formally annexed by Great Britain ten years after they had installed Akitoye as the Oba of Lagos. Akitoye himself had spent a good portion of the decade between 1841 and 1851 in Europe after many elites in Lagos opposed him becoming Oba due to his pro-British commitment to the abolition of the slave trade. That level of direct experience of the Atlantic world--of travel to Europe or the Americas or both--was not limited to Akitoye. At the height of the Atlantic slave trade and the subsequent "era of legitimate commerce" between 1770 and 1880, a significant number of West African commercial elites and political elites travelled abroad and came back again, some involuntarily (taken as slaves), others as emissaries or agents of European mercantile companies or governments.

Even those who had not travelled personally generally had considerable direct contact with European merchants, missionaries and diplomatic representatives in the trading districts where they lived in coastal Atlantic ports and cities. Quite a few of those West African elites were at least partially literate in English, French, or Portuguese, some far more so. There were quite a few men like Samuel Ajayi Crowther and Samuel Johnson, "recaptives" who were from southern Nigeria or nearby but who grew up in Freetown Sierra Leone and were missionaries and authors (Johnson wrote an important history of the Yoruba people and the Oyo civil war), though Crowther and Johnson were obviously extraordinarly talented individuals.

There were societies in southern Nigeria that were less connected to the Atlantic trade and were therefore less familiar with Europeans and European affairs, certainly. But even the novelist Chinua Achebe may be overstating a bit the degree to which European presence was a relatively new or unfamiliar thing in his famous novel Things Fall Apart. (Though Achebe is primarily focused on the coming of Europeans as imperial conquerors, which did not happen in much of southern Nigeria until the 1870s-1880s.)

Anywhere that was strongly tied into the Atlantic world in this part of West Africa, commercial and political elites had a fair working knowledge of Western Europe and the wider Atlantic world by 1840-1850, often much earlier.

For a detailed sense of this, Randy Sparks' Where the Negroes Are Masters, about the trading port of Anomabu in what is now Ghana will give a clear picture of the cosmopolitanism of Atlantic West African elites in this time period.