They might ask you when the last time you ate anything.   If you know you have diabetes then you should be on a sugar free diet, so by the time they draw blood, having eaten won't make a lot of difference.  

I always just tell them I haven't eaten anything in about four hours and it seems to satisfy them.  

Truth is I usually drink a couple cups of coffee with lots of cream and sugar, just before I go to the doctors office.   My glucose is still usually within normal range and the few times it was a little high, I know what caused it.  They never say anything and don't seem to be concerned about it.  If they ever would say my glucose is a little high, I'll tell them my glucose level if fine  considering I ate a ton of sugar in coffee, on my way to the doctors office. If I hadn't consumed the sweet coffee, it would've been within normal range.   I call it my glucose tolerance test. 

Doubt it, they would probably just do a general blood test and only ask you to fast for a follow up if that suggests your sugar levels are out of control.

The office will let you know. Call them as you are concerned.

You will have to fast if the doctor ordered blood tests. BTW coffee will spike your blood pressure.