Are you from the UK? Just because of the username/use of "cheers"
If you are, then I would post this question in the UK nursing forum because I've only seen one or two UK nurses in this particular forum and there are a lot of senior nurses posting in the UK forum. I believe you do a Msc in Neonatal Nursing, but I wouldn't quote me on that. I've done a little bit of research because I may move to the UK in a few years (my husband is from the UK), but I haven't really looked that much into NP stuff, although I know that the UK doesn't have a licensing body for NPs.
If you are in the US, you complete at least 2 years in a level III NICU at bedside and then complete a neonatal nurse practitioner degree (either MSN or DNP). There is a list of all the NNP programs known at the bottom of this page in one of the stickies.