De or het nevenvordering?

The correct Dutch article is:

de nevenvordering

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

How to use nevenvordering

the nevenvorderingde nevenvordering
this nevenvorderingdeze nevenvordering
that nevenvorderingdie nevenvordering
our nevenvorderingonze nevenvordering
your nevenvorderingjouw nevenvordering
every nevenvorderingelke nevenvordering
which nevenvordering?welke nevenvordering?
a big nevenvordering / the big nevenvorderingeen grote nevenvordering, de grote nevenvordering