Which country operates the most Monero nodes per capita?
Do miners in countries with the most nodes have an advantage due to better average network propagation times?
The distribution of nodes varies over time and not all nodes are visible
https://monerohash.com/nodes-distribution.html Currently the United States has more publicly visible nodes than any other country. However that does not mean that US residents control the most nodes. Since nodes can be hosted remotely and run on VPS, nodes with an IP located in one country can be controlled by someone living in another country across the world.
Network latency can be influenced by geography but there are other factors involved. The increase from 1 to 2 minute blocks helped to level the playing field for miners with slightly worse network latency (and also has helped decrease the frequency of orphaned blocks). It is also worth noting that not every node is a miner.