Ooh good luck. I'm sure you will do well if you have a lot of experience as a coordinator as I'm sure you 'get' what's needed and that's half the battle!
When I interview for advisers in terms of technical knowledge, I want to see that they understand the fundamentals of employment law (fair reasons for dismissal, what a 'fair process' looks like in terms of a disciplinary, grievance, appeal etc, how the basics of things like annual leave, sick pay etc works - all things you can get from ACAS or your organisation's handbooks/policies). I want them to understand how our payroll/employment record/recruitment systems and software works, that they can understand and use a basic excel sheet and can read/interpret simple charts like a sickness absence trend graph (you'd be surprised how many people in HR can't!) and talk to that in terms a manager would understand and make basic recommendations for improvements. I want them to be able to understand and apply our policies but crucially also be able to 'problem solve' for managers and staff, e.g. how to explain policies so people understand, know where it is really important a policy is followed to the letter and where it's more of a guideline and when/how something should be escalated higher for resolution.
Softer skills I would ask about are customer service, conflict resolution, team working, time management/prioritisation, ability to work under pressure, negotiation/persuasion skills, ability to communicate complicated concepts in terms non experts will understand.
I don't tend to ask 'scenario' questions myself so much as I ask people for examples from people's own experience, but you might get ask general ones like 'a member of staff is off sick/accused of misconduct/goes AWOL/asks how much leave they'd be entitled to if they go part-time', kind of testing your policy knowledge kind of ones. Or if they are going to challenge you a bit more they might ask some more difficult ones about unusual or complicated situations. Some examples of the types of things that might come up are below. The thing to remember with this type of question is there isn't always a single right answer so don't panic if you are not sure exactly what you would do or feel you need more information, they are more looking to understand your general approach, i.e. will you always prioritise customer service/staff wellbeing, do you know when/how to escalate when something is beyond your control, are you a team player, do you know how to manage conflict/complaints etc? I think in response to a scenario it's fine to say something like 'well I would ask for/find out more information on ABC, if A I would do this, if B I would do this, I would also consider if C or D was appropriate in line with the organisation's priorities' rather than feeling you have to say just A or B, if they push you for an unequivocal answer then you can then say that A is usually the best or whatever.
-A difficult/angry manager who won't listen to your advice/wants to do something outside of policy, what do you do?
-An upset member of staff who's had a bad experience (bullying/harassment/discrimination) but doesn't want to make a formal complaint/wants to stay anonymous, what do you do?
-A member of staff asks a complicated question about sick pay/holiday pay/overtime and you can't find the answer anywhere in policy, what do you do?
-A member of staff/manager calls up and is very upset/angry about something recruitment/L&D/OH or anything else outside your control has done, what do you do?
-You have a really high workload with lots of emails, phone calls coming in, a report deadline, some policy updates to do and then a member of staff turns up in tears, how do you manage this/prioritise? (Follow up might be dealing with the emails/calls/member of staff takes so long that you realise you can't finish the report in time, what do you do?)