"What is the date of the celebration?"
Translation:Quelle est la date de la fête ?
"de la" is never contracted to "du" - "du" is a contraction of "de" and "le" (masculine singular definite article, before a word that doesn't start with a vowel or "silent" h), whereas "la" is feminine.
- de + le = du
- de + la = de la
- de + l' = de l'
- de + les = des
If "Quelle date somme nous" means what day is this, why do we have to say "Quelle est la date..." in this case?