Self-questioning ... Jonathan Franzen

A curious thing about the Frankfurt Book Fair, where I've been ensconced for the past week, is the relatively low profile of those people without whom there would be no books to fair-y about with - the authors. While there is a smattering of German writers and the occasional big international name (Umberto Eco made an appearance on the "blaue sofa" this year) the fair is fundamentally about the book trade circus - agents, publishers, marketers - rather than the creators.

So it comes as a surprise to turn a corner in the International Centre and suddenly come face to face with the images and voices of some of the world's most renowned writers. The huge black and white close-up portrait photos are accompanied by a set of headphones. Put them on and you hear an intriguing dialogue. "Mr Kertesz," says Imre Kertesz, "Your time is nearing its end. Are you satisfied? No." Or, "Well, Frank McCourt, do you believe in God?" or "Zadie, what do all three of your books have in common?"

It's the brainchild of Tobias Wenzel, an affable German radio journalist. He explains that while conducting a series of literary interviews a couple of years ago he would sometimes reach the end of the interviews and sense a certain disappointment in his interviewees that he hadn't asked them a particular question. From then on he decided to end every interview with the query, "What is the question you've always wanted someone to ask you?"

He recorded the replies and the result is this exhibition, which puts together the "my question for myself' of a selection of them - the project took on a life of its own and he has over 90 subjects now - with their portraits.

The arresting photographs are the work of Carolin Seeliger. She focuses on the eyes of her subject so that although the size and concentration of the photo is technically unforgiving (Paul Auster, alone among the interviewees, apparently demanded that he be allowed to wear sunglasses as he was worried about his wrinkles), the gaze of the viewer is drawn, almost, it feels, into the subject's mind.

The combination works perfectly. The Icelandic writer Hallgrimur Helgason stares intently out, a slight smile playing on his face. "Mr Helgason, do you want anything else," he asks. "Yes, another two lives, please!" A slightly worried-looking but clearly very in-the-moment Jonathan Franzen wonders why he is so agreeable when people ask to take his picture (and in a lengthy reply decides that "the more you show of yourself the more protected you are"). Richard Powers' answer to his question, "What is evil?" is also fairly involved and I ask Tobias if any national writerly characteristics have emerged. Do Americans tend to be more verbose?

Not necessarily, but they are always super-professional about it, he says. What the American and English writers do have in common, he says, laughing, is that they always begin their answer with the joke, "That's a very good question!"

Some of the questions are also perfectly in authorial character. Umberto Eco, interviewed at the fair, offers "Umberto Eco, is this a question? Yes."

The British author William Boyd was one of the interviewees (he asks himself about the influence of Africa on his work) and was so taken with the project that he will be featuring it next spring in an edition of Granta which he is guest-editing. The exhibition is to travel around other book fairs next year and will eventually be made into a book.

Of course, at the end of my chat with Tobias, I have to turn the tables on him. "Tobias, what question would you have liked me to ask you?" He's obviously thought about this and answers, quick as a flash, "Tobias, is there life before death?" he pauses, "I'm not sure."

So, over to you. What question have you always wanted to ask yourself? Questions and answers here, please...