De or het ego-psychologie?

The correct Dutch article is:

de ego-psychologie

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

How to use ego-psychologie

the ego-psychologiede ego-psychologie
this ego-psychologiedeze ego-psychologie
that ego-psychologiedie ego-psychologie
our ego-psychologieonze ego-psychologie
your ego-psychologiejouw ego-psychologie
every ego-psychologieelke ego-psychologie
which ego-psychologie?welke ego-psychologie?
a big ego-psychologie / the big ego-psychologieeen grote ego-psychologie, de grote ego-psychologie