De or het treinsamenstelling?

The correct Dutch article is:

de treinsamenstelling

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

How to use treinsamenstelling

the treinsamenstellingde treinsamenstelling
this treinsamenstellingdeze treinsamenstelling
that treinsamenstellingdie treinsamenstelling
our treinsamenstellingonze treinsamenstelling
your treinsamenstellingjouw treinsamenstelling
every treinsamenstellingelke treinsamenstelling
which treinsamenstelling?welke treinsamenstelling?
a big treinsamenstelling / the big treinsamenstellingeen grote treinsamenstelling, de grote treinsamenstelling