This works for me 100% of the time, it works like a charm. I always ask the girl.
Me: Excuse me i'm sorry but I don't want to mis-pronounce your name. Can you tell me how you pronounce your name the way you like it?
Her:Jessica, but I like it when my friends call me Jessy.
You see you can even get added information with this one about the way she likes her friends calling her name. This never fails, I don't give a fuck what anyone says about this. I love it. 100% Jacked

You see there are so many girls out there with names that can be pronounced so differently. Like this one time a girl I forgot her name, it was RACHELLE.
Me: Sorry but can you tell me how you like your name to be pronounced?
Her: Rachelle, most people pronounce my name like Rachel but I hate it. Its Rachelle.
Me:Ya I would of definitely been calling you Rachel thanks, Rachelle.
You see she pronounces it (Rah'chelle). I hope this helps people.