If it's European in origin, then it would be "D"- "nahn".
Vowels in European names are shorter sounds.
The Euro vowel "i" is pronounced as our American "e" sound, thus
"D-i" would sound as simply the American letter "D".
"nan" would have a short "ah" sound unlike the American "a" sound, as in the name "Ann" which is a nasly sound not consistent with European pronunciations of the vowel "a". So, it wouldn't be "n-ann" sound, but rather "n-ahn".
But, if the guy is American, then the pronunciation would be whatever
he says it is as most Americans have butchered the pronunciation of their European sur names.
"Porsche" is a 2 syllable word and he was not German. "Porsch" is not how it's pronounced.
Whatever.
TT