How can I force Node's request module to not encode the response?

The encoding has nothing to do with request. StackOverflow's API returns GZip encoded data always, as explained in the API documentation. You need to use Node's zlib module to unzip the contents. This is a simple example:

var zlib = require('zlib');

// Other code

, function(err, response, body) {
   zlip.gunzip(body, function(err, data){
     console.log(data);
  });
});

The main downside of this, which is bad, is that this forces the request module to process the entire response content into one Buffer as body. Instead, you should normally use Node's Stream system to send the data from the request directly through the unzipping library, so that you use less memory. You'll still need to join the parts together to parse the JSON, but it is still better.

var zlib = require('zlib');
var request = require('request');

var apikey = '<MyKey>';
var fromdate = '1359417601';
var tagged = 'node.js';
var compressedStream = request('http://api.stackexchange.com/2.1/questions?' +
    'key=' + apikey + '&site=stackoverflow&fromdate=' + fromdate +
    '&order=desc&sort=activity&tagged=' + tagged + '&filter=default');

var decompressedStream = compressedStream.pipe(zlib.createGunzip());

var chunks = [];
decompressedStream.on('data', function(chunk){
  chunks.push(chunk);
});
decompressedStream.on('end', function(){
    var body = Buffer.concat(chunks);

    var data = JSON.parse(body);

    // Do your thing
});

First set accept: identity as a header. If stacked change doesn't send data as regular UTF8, then it's a bug on their end.

Secondly, you want to set the encoding as UTF8 so the response isn't a buffer.