I am guessing that 'starà' is the future form, since it is very similar to 'sarà', future of 'essere'. If I'm right, wouldn't this mean "What will be happening?" It seems like "What can be happening?" would need a different verb, maybe 'possere', if I have that infinitive right. I'm confused.
I knew that 'stare' was the right auxilliary, I just wondered why it wasn't translated in the future tense when 'starà' (which I hadn't seen before) seemed to be the future of 'stare', since it looked so much like 'sarà', which I had seen before. Thank you for your explanation that in Italian it can be used in this conjectural sense, too. :)