Final answer:
The most suitable activity is a collaborative arts-based project that encourages social interaction, skill-building, and community contribution. It should be structured to support social communication in a group setting.
Step-by-step explanation:
The most appropriate activity to include in a social skills group for individuals functioning at the project group level, designed by an Occupational Therapist (OT), would be collaborative group activities that engage participants in shared objectives and foster social interaction. An example could be organizing an arts-based project where members work together to create something positive for the community, such as the 'positive signs project' or engage in the development of an art piece that encourages self-healing and relationship-building. It's important that the activity provides an opportunity to practice social communication skills in a supportive and structured environment, which might also feature components of applied behavior analysis (ABA) to promote learning and engagement.