De or het gehooropening?

The correct Dutch article is:

de gehooropening

Rule Words ending in -ing: almost always de. See the rule

How to use gehooropening

the gehooropeningde gehooropening
this gehooropeningdeze gehooropening
that gehooropeningdie gehooropening
our gehooropeningonze gehooropening
your gehooropeningjouw gehooropening
every gehooropeningelke gehooropening
which gehooropening?welke gehooropening?
a big gehooropening / the big gehooropeningeen grote gehooropening, de grote gehooropening