ChrisMwn and EGoodhue, do you know this one? Otherwise, he should probably check with INZ if he is allowed to do this. I'm not sure if apprenticeship (learning in with working) would count as studying, and the factsheet says up to 3 months' study is all right.
https://www.immigration.govt.nz/new-...s-visa-holders
He would be clear to do this on a residence visa, and he wouldn't HAVE to wait till the end of the present work visa to apply for that - he could put in the application as soon as you have 12 months' evidence of partnership.