Personally, I would say it's easier to learn routes if you already know the area a bit, and you will get passenger asking whether your bus goes to some place you've never heard of and isn't an official bus stop name, and it turns out to be the name of a pub that was demolished 10 years ago, and that sort of thing.
Having said that, there are plenty of people driving buses now and in the past who have moved country as well as town and got a job on the buses.
I know almost nothing about Newport or Newport Buses, but any reputable operator will offer route learning (as Eyersey468 has said) - this could involve video footage and written material with pictures of particular hazards to look out for (watch out for the trees on this road, the bus lane approaching that junction is just too narrow for a bus, you need to start steering at the exact moment the front of the bus is level with this lamp post to get round this awkward bend, and DON'T GO UNDER THAT LOW BRIDGE sort of stuff) as well as going out and seeing it from a bus.
Traditionally, new drivers were sent out to travel passenger on service buses to do route learning, it's becoming more common to be taken out driving the route with an instructor or experienced driver. Different people learn in different ways, and the latter makes it a bit hard to make notes or draw lines on a map or anything like that.
Are you going in as an existing PCV licence holder or a full trainee? Some operators might prefer someone who has a PCV but might need a bit more route learning than someone who needs full training.
Either way, if you find you're not comfortable with it all after initial route training, it's worth saying something - they would probably prefer you to have a bit longer on route learning rather than risk you getting lost / having accidents - although they might expect you to do some of it in your own time. (I once met a London Transport driver who would walk the entire route which must have taken a bit more time than LT allowed!)
Don't know enough about Newport Buses to say how they bring new drivers in. The traditional was that new drivers went 'on the spare' so could be expected to do more or less any route with any type of bus at a moment's notice on any day. Many operators now do try to give drivers an easier start - maybe starting off on a relatively simple route (or small group of routes), and / or having a week or so driving in service but with an experienced driver (some call it 'mentor' but the language varies) on the bus.
Best of luck.