Reading data from ThingSpeak via Arduino Uno+ESP8266
HTTP GET request needs to end with an empty line and HTTP 1.1 requires a Host header.

Add an empty line and eiher change the HTTP version to 1.0

client.print("GET /channels/421932/feeds.json?api_key=");
client.print(apiKey);
client.println("&amp;results=2 HTTP/1.0");
client.println(); // empty line


or add the Host header

client.print("GET /channels/421932/feeds.json?api_key=");
client.print(apiKey);
client.println("&amp;results=2 HTTP/1.1");
client.print("Host:");
client.println(host);
client.println(); // empty line