De or het viewing?

The correct Dutch article is:

de viewing

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

How to use viewing

the viewingde viewing
this viewingdeze viewing
that viewingdie viewing
our viewingonze viewing
your viewingjouw viewing
every viewingelke viewing
which viewing?welke viewing?
a big viewing / the big viewingeen grote viewing, de grote viewing