De or het diplomasupplement?

The correct Dutch article is:

het diplomasupplement

Rule Words ending in -ment: usually het. See the rule

How to use diplomasupplement

the diplomasupplementhet diplomasupplement
this diplomasupplementdit diplomasupplement
that diplomasupplementdat diplomasupplement
our diplomasupplementons diplomasupplement
your diplomasupplementjouw diplomasupplement
every diplomasupplementelk diplomasupplement
which diplomasupplement?welk diplomasupplement?
a big diplomasupplement / the big diplomasupplementeen groot diplomasupplement, het grote diplomasupplement