I just say it as it's written, a one-syllable Jvan. Literally 'van' with a 'J' at the beginning. The J kind of melts into the V - and it does so quite well. Much easier than saying knight how it is spelt.

As for Y'van, which is what the Vetruvians call her. I actually pronounce it 'Ee-van'. Our local Jvan Evans.