Remote operation of highly automated vehicles (HAVs) may include occasional assistance from a human remote operator that is located outside the HAVs. Remote assistance typically delegates only highlevel guidance tasks to the remote operators such as authorizing a driving maneuver or specifying a new driving path. As remote assistance is fairly unexplored, there are still several research challenges. These challenges were discussed by experts from academia and industry in a multidisciplinary workshop at the 2023 IEEE Intelligent Vehicles Symposium. As a result of the workshop, this paper presents a list of most pressing research questions in the following areas: human-machine interaction and human factors, design of the remote station, design of the HAVs. It also outlines a roadmap for future research on remote assistance of HAV, thereby informing interdisciplinary studies and facilitating the benefits of HAVs before full autonomy can be reached.