my first HR job was NHS recruitment. i can't remember what i was asked as it was 20 years ago, but here are a few pointers as to what you may be asked;
prioritising your work - you'll have lots of different roles to work on, all at different stages of the recruitment process eg advertising roles, organising interviews, pre employment checks etc. So you'll need to consider how you prioritise your work. Tasks like setting up interviews are a priority because you'll need to give candidates enough notice, otherwise they may not be able to attend the interview and rescheduling may make it difficult for the panel to attend.
customer services - working with difficult managers (they all want their jobs filled yesterday), so have to manage their expectations.
pre-employment checks - as it's NHS, there will be lots of checks for new appointees eg 2 references, right to work, checking professional registrations, health checks. you can learn what these are on the job, but it's hugely important, so it's worth swotting up on why you need to complete them.
safeguarding - linked to the pre employment checks. they may ask you about your understanding of safeguarding both in general, but specifically about your role - resourcing is the gatekeeper of the organisation and you shouldn't be letting anyone work without the pre emolument checks having been completed.
Diversity - they may ask about your understanding of diversity both in general, but specially related to the role eg they could ask you about your understanding of reasonable adjustments for interview - this could be a physical adjustment eg access to a lift or someone asking for the interview questions in advance because they have dyslexia.
good luck.