How to pronounce acronyms and initialisms with apostrophes?
I think typically you would follow the rules of pronunciation given the last letter of the acronym. So as mgb says, in your example it would be "En Aye Aitch ez". Some other examples:
The US's: "The You Ess ez"
The USA's: "The You Ess Ayz"
The UK's: "The You Kayz"
The CBC's: "The Cee Bee Ceez"
If the acronym is one that you read like a word, such as NASA, then you would follow the rules for words.
NASA's: "Nassaz"
And so forth.
i would pronounce it "N I H -es" ie "en hi aitch ez"