De or het studieplanning?

The correct Dutch article is:

de studieplanning

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

How to use studieplanning

the studieplanningde studieplanning
this studieplanningdeze studieplanning
that studieplanningdie studieplanning
our studieplanningonze studieplanning
your studieplanningjouw studieplanning
every studieplanningelke studieplanning
which studieplanning?welke studieplanning?
a big studieplanning / the big studieplanningeen grote studieplanning, de grote studieplanning