This skill connects directly to the NYC MTA's *realtime* data feed for the 1, 2, 3, 4, 5, 6, A, B, C, D, E, F, G, L, S, J, Z, N, R, W, and Q trains. You can ask it when the next train is coming for a specific direction and station such as "Ask NextSubway when is the next uptown 6 train at Union Square?" and Alexa will respond "The next uptown 6 train arrives at Union Square in 2 minutes, 12 minutes, and 23 minutes". You can then plan your walk to the subway station accordingly!
“Alexa, ask NextSubway when is the next Manhattan bound L train arriving at ... ”