De or het knotsoefening?

The correct Dutch article is:

de knotsoefening

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

How to use knotsoefening

the knotsoefeningde knotsoefening
this knotsoefeningdeze knotsoefening
that knotsoefeningdie knotsoefening
our knotsoefeningonze knotsoefening
your knotsoefeningjouw knotsoefening
every knotsoefeningelke knotsoefening
which knotsoefening?welke knotsoefening?
a big knotsoefening / the big knotsoefeningeen grote knotsoefening, de grote knotsoefening