As an interviewer, what are some effective interview questions, would you recommend, to ask candidates for a role in Graphic Design?

I think Rami's suggestion above is excellent and Raphael's comment is very important too. So my suggestion should be taken as an addition to those. 

Typography is often overlooked, especially by those without a solid graphic design training.

So I would ask them to outline the difference between a display font and a text font. Perhaps they could provide an example of their favourites and explain what they like about them.

When interviewing for a graphic design position, first u need to ask questions that relate to the creative aspect of the job to ensure that it would be a good fit for your personal design style, then ask about computer systems in use at the company and what applications you are expected to be proficient in. 

What is more important within perception, what the eye can see of the object or what the mind knows about the object?

I would ask him to simulate ''life'' an brief creative design just to know his creativity limit.

You may be asked to describe previous projects.

Tell me about some of the designs you have created, and their success.How do you plan your designs before you start drafting them?

Do you sketch your designs first before converting them to digital format?

How well do you take criticism?

How comfortable are you being told what to design?Graphic design interviews will focus a lot on all stages of the design process.

Expect several standard interview questions in addition to the questions above.

I would love to know the amount of creativity the candidate possesses. Ofcourse, He/She can choose to present their work or portfolio to get a better understanding of their style and approach which would be great. Other than the fact , other questions solely depend on the job and position they are applying for and what they can do to be the best in that and in favor to the company.

I never interviewed any creative for recruitment but I have been interviewed a lot of times for various projects. Situational questions always occur, like "how do you deal with difficult clients?" or "how do you handle deadlines?" They don't delve in technical questions because portfolio already speak for themselves. Employers are often interested with our problem solving skills and creative process. I've been asked "what are your hobbies?" and "what do you do to relax?", weird as it seems but they just want to see what inspires our art / design without being straight forward.

Many of a good questions are their in our sit (beyt.com) related wth Graphic designs have been given by our colleagues that were very good questions for candidates.

don't ask him knowledge questions, ask him to know his creativity

example provide him with4 color palettes and make first palette Wow, the second good, third one bad & final one very bad. then ask him to choose wonderful one, then let him choose the very bad one and you will know is he useful for you or not...

?Graphic designer what can be designed

what's the difference of CMKY  color and PANTONE color and which is more cost effective.