De or het weekopening?

The correct Dutch article is:

de weekopening

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

How to use weekopening

the weekopeningde weekopening
this weekopeningdeze weekopening
that weekopeningdie weekopening
our weekopeningonze weekopening
your weekopeningjouw weekopening
every weekopeningelke weekopening
which weekopening?welke weekopening?
a big weekopening / the big weekopeningeen grote weekopening, de grote weekopening