Most te reo speakers today will pronounce it like this, which is pretty close to how you're spelling it out! https://maoridictionary.co.nz/search?idiom=&phrase=&proverb=&loan=&histLoanWords=&keywords=ngaio

But the 'ng' at the start can really vary across the country, with different iwi pronouncing the consonant differently: Lake Wanaka in south island comes from the māori word "wananga" (wisdom), as Ngāti Tahu pronounce the 'ng' more like a "k" than a "n".