What stage are you at? Have you been diagnosed? Or had tests before? The questions you'll want to ask will really depend on this, as there's not much point asking about treatment if you don't even know what is wrong with you yet. And if you've already had some tests run (e.g. blood tests by the doctor who referred you to the specialist) you might want to discuss the significance of the results, whereas if you've had none you'll want to know where to start.
So if you can post some more details about your situation, we can suggest to you some questions you might want to ask.
More generally, you might want to ask for a timeframe - when you'll see the specialist again, etc. - and bring up any symptoms which are particularly troubling to you.