What approach involves looking at manuals for existing similar products?

The correct answer centers around the method of utilizing manuals for existing similar products, which is categorized under studying documentation. This approach allows designers and developers to gain insights into how similar products function, their features, and user interfaces. By examining manuals or documentation, one can discern best practices, identify usability issues, and understand how users interact with those products. This knowledge can then inform better design decisions and enhance the overall development process for new interactive designs.

Researching the competition primarily involves analyzing competitors' products in the market rather than focusing solely on their documentation. While both approaches can be valuable, studying documentation specifically emphasizes the understanding gained through existing auxiliary materials like manuals. Mapping typically refers to creating visual representations of processes or systems rather than studying existing manuals. Feedback focuses on gathering inputs from users or stakeholders about a product's performance, which does not directly involve existing product documentation. Thus, studying documentation stands out as the most relevant and effective approach in this context.