De or het portrettering?

The correct Dutch article is:

de portrettering

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

How to use portrettering

the portretteringde portrettering
this portretteringdeze portrettering
that portretteringdie portrettering
our portretteringonze portrettering
your portretteringjouw portrettering
every portretteringelke portrettering
which portrettering?welke portrettering?
a big portrettering / the big portretteringeen grote portrettering, de grote portrettering