De or het stamboomforum?

The correct Dutch article is:

het stamboomforum

Rule Words ending in -um and -ium: usually het. See the rule

How to use stamboomforum

the stamboomforumhet stamboomforum
this stamboomforumdit stamboomforum
that stamboomforumdat stamboomforum
our stamboomforumons stamboomforum
your stamboomforumjouw stamboomforum
every stamboomforumelk stamboomforum
which stamboomforum?welk stamboomforum?
a big stamboomforum / the big stamboomforumeen groot stamboomforum, het grote stamboomforum