What is the proper pronunciation of this sentence as an event organizer?
This is the example:
Je suis Joana l'organisateur de l'événement, quand est la date exacte de l'événement ?
Here is how to pronounce "l'organisateur de l'événement"
But if you are a girl, you could say "l'organisatrice de l’événement"
It is pronounced as documented in the dictionaries:
IPA /lɔʁɡanizatœʁ də levεnmɑ̃/
There might be language register or regional variations. For example the e in de might be mute ( /dlevεnmɑ̃/ ) and while the e located before -ment in événement is mute in standard French, it is generally pronounced in southern France; -ment might also be pronounced /mɛ̃ŋ/ there.
Note that (safely) assuming Joana is a feminine first name, that should be l'organisatrice de l'événement.
Événement is written using the traditional spelling which doesn't match its pronunciation. A new accepted spelling is évènement.
As Grep pointed out, there is an adverb mismatch. That should be either:
Quelle est la date exacte de l'événement.
or, keeping quand:
Quand exactement aura lieu l'événement