You can programmatically add questions using PHP code. Start here: http://docs.question2answer.org/code/external/
Create a PHP script that takes parameters of title, content, tags etc and use those to add a new question. I don’t know exactly how IFTTT works but if it does POST requests you’d get the parameters from $_POST['title'] for example. Then you’d tell IFTTT to load your script (example.com/addquestion.php).
For the userid you’d presumably have a special user set up.
IMPORTANT: add some security like an API key that must be provided to add the question. Otherwise anyone could add questions without being logged in.