Hi @armingrudd,
Did you take a look at this post Determine the right number of clusters?
It links to one of our examples (https://www.knime.com/nodeguide/control-structures/loops/loop-over-a-set-of-parameter-for-k-means). This is a pretty straight forward way to it by simply trying out different number of clusters and comparing their entropy scores.
Cheers,
Simon