How to score a 100-fold capacity increase in an energy-efficient way? How to address privacy and security concerns specific to the convergence of communication and sensing? How to design semantic-aware communication protocols? These are some of the key research questions to be answered in the transition toward 6G, according to the 6G-RIC Research and Innovation Cluster (6G-RIC) research roadmap. At the heart of 6G-RIC are six Technical Innovation Areas (TIAs), which serve as technology drivers for 6G. Each TIA is associated with specific research challenges, whose resolution lies at the focus of the 6G-RIC research agenda. In this document, we formulate these challenges in the form of key research questions that should be answered within each of the six TIAs. Due to the interdisciplinary nature of the selected questions, 6G-RIC undertakes a holistic approach that simultaneously investigates hardware architectures, signal and protocol design, network computing aspects, as well as algorithmic and implementation complexity. In this context, energy efficiency and security play a leading role as horizontal aspects overarching all studied technologies.