Hiring managers at Omnicom Group want to understand if, as a media buyer, you have specialized in purchasing a particular type of media. A thorough understanding of the different media platforms is valuable when working with Omnicom Group's clients as placement, timing and price is negotiated.
If you have expertise with a particular type of media, be sure to mention that in your response. The company would like to evaluate if your expertise with a specific media type matches up to the needs of its clients. If you have experience working with several media types, highlight that as well. Omnicom Group's hiring managers will likely look at that favorably as it will indicate your flexibility as it relates to placement on client projects.