De or het netwerkplanning?

The correct Dutch article is:

de netwerkplanning

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

How to use netwerkplanning

the netwerkplanningde netwerkplanning
this netwerkplanningdeze netwerkplanning
that netwerkplanningdie netwerkplanning
our netwerkplanningonze netwerkplanning
your netwerkplanningjouw netwerkplanning
every netwerkplanningelke netwerkplanning
which netwerkplanning?welke netwerkplanning?
a big netwerkplanning / the big netwerkplanningeen grote netwerkplanning, de grote netwerkplanning