Hi
I wouldn't worry too much about which books you have or haven't read. An interest in retail design, FMCG and retail in general might do it. For a retail gig they're more likely to be interested in your knowledge of creating artwork for retail, point of sale, large format displays, window vinyls and the like. Knowledge of preparing and sending artwork for print. Maybe experience of Adfast. Maybe magazine or catalogue work (if they produce these in-house). These kind of jobs can have a heavy workload deadlines around new product launches. If it's a national chain you may be expected to develop regional versions of national campaigns.
In general stress how well you can take a brief and scale it up as required, how well you traffic workflow in a busy studio enviroment and what an exciting field mobile comms is at the moment (whether you believe that or not). Much of the material in these stores is prepared by the individual ad agencies who are running campaigns for the individual brands (Nokia, Apple, HTC etc) not the retailers. You may be expected to integrate these pre-existing marketing assets into dual-branded pieces for your employers use while being aware of the individual manufactures sensitivity to dual-branding. A knowledge of shop fitting displays and retail branding terminology (wobblers, tents, shelf-abrkers etc) can't hurt.
Remember to ask how their studio is currently structured so you have an idea of what the role expects and how much of a creative lead they expect you to take. This will allow you to tailor your answers accordingly as you don't want to come over as some tortured auteur if what they want is a jobbing artworker who can manage the grind. Good luck.
