Im a senior NHS manager working at sub board level, so I work with exec and other types of directors. I work with PAs and Exec PAs to get things done and on time.
PAs/Exec PAs are crucial for diary management and getting the days to run smoothly. They are also crucial for reminders to staff to ensure they know and are reminded to get tasks done by deadlines.
Making sure director has papers printed off and ready for meeting or available on their laptop to view is also crucial or they can't function in meetings.
Meeting minute taking is important, noting down key discussion points, actions agreed, decisions made etc.
Microsoft Office is important particularly Word and email. They may have a software system for creating meeting agendas and attaching the required meeting papers. Just ask them if they use anything specific and what its name is. Say with your general IT knowledge that you're sure you will pick that up fairly quickly after being shown.
Emphasise that you're approachable, professional etc - so can deal effectively with staff at all levels and staff groups in organisation and deal with those external such as MPs, police, families etc.
Tell them you can multitask and are resilient - cope under pressure. It really is a job that has a lot if things going on at once.