Someone may be along who can go in to more detail on the specifics, but from past railway interviews...
They will probably ask a question or two to see if you know about how the railways are regulated and run, as in relationships between DfT, Network Rail, Train operators and so on. And about their network. (I would not expect detailed questions like what sort of unit works a specific line, or track layouts at specific stations or anything like that, but a knowledge of some of the key places, key passenger markets, some of the special events their network caters for might help.)
Increasingly, interviews are 'competency based' so questions like 'tell me about a time you did X' or 'give an example of a time you did Y' are likely. And the skills and experiences these are likely to about are the things listed in the job advert or whatever as essential / desirable skills or experience (you've seen the job advert / job description or whatever they call it, I haven't.) Generally, interviewers prefer one good example rather than a handful of examples, so it's worth thinking of suitable examples that match the skills etc they have listed.
arguably, this is unfair to people who have a wide range of experience they might want to demonstrate and favours people who can talk up one situation more confidently, but...
It can be worth trying to think of examples from different jobs and using different jobs for different answers if you can - that can bring out a range of experience.
If you've not met the concept, look up
STAR method for interviews - Situation is about what the organisation / team was setting out to do, but the interviewer wants to know what you as an individual did.
Some might advise it, but personally, I'd say not to try and memorise an answer word for word, as the questions won't always be exactly what you're expecting - there may also be a twist like 'and what did you learn from it?' or 'and what would you do differently if it happened again?'
There can be circumstances where a situation or experience from voluntary work or education is a relevant answer (you say 'apprentice' so my first assumption is you're fairly young, but my second thought is that's not always the case now) - the railway related work may be relevant, but if it's a business / admin related job, then experience from other jobs may be more relevant to at least some of it.
Even for a job that's office rather than operational there may be a safety related question - so may be worth thinking about how you've followed safety related rules / procedures in past jobs - doing gateline and rail replacement (controller?) will have had some aspects from that. You might get a question about a time you've prevented or dealt with a safety incident.
Hope it goes well.
