De or het parallelsessie?

The correct Dutch article is:

de parallelsessie

Rule Words ending in -tie and -sie: almost always de. See the rule

How to use parallelsessie

the parallelsessiede parallelsessie
this parallelsessiedeze parallelsessie
that parallelsessiedie parallelsessie
our parallelsessieonze parallelsessie
your parallelsessiejouw parallelsessie
every parallelsessieelke parallelsessie
which parallelsessie?welke parallelsessie?
a big parallelsessie / the big parallelsessieeen grote parallelsessie, de grote parallelsessie