It's kinda hard to tell you what to ask since I don't really know where you are in life. Are you an undergrad, grad, returning student?
Personally I would ask them the following questions: how they choose their career, what are the ups and downs of their job, do they have difficulty balacing work and personal life (maybe phrase that question differently), what did they think of vet school, what kind of personal traits do vets need to have according to them?...all these will help you decide if being a vet is right for you, but also make sure you see some procedures and surgeries. I had a friend who could not stand the sight of blood and nearly passed out in surgery.
All those things are important but ultimately what I would do is figure out which careers appeal to you and maybe shadow an individual in each career for 1-2 weeks and then decide which career to pursue.
One more thing I will add, is that make sure you want to become a vet before starting vet school b/c you need to be dedicated when you start school otherwise you are going to hate it.
Good luck with everything!