Do yourself a favour and switch to using Express which will provide you a better structure for mucking about with inbound requests.
Here you have not processed the request.query into an array to use.
You can use URL to do this
for example
const url = require('url');
var parts = url.parse(request.url);
var challenge = parts.query[“hub.challenge”];
console.log( `challenge: ${challenge}` );
Should suffice. But express will save you time and effort