Give a max. DC it can target, perhaps 40, higher would be 'too complex'

Knock should open all mundane locks. It is no more than fair, for a Wizard who memorized a Knock, that it would work. It's a valuable spellslot, and in 99,9% of the occassions, the Knock spell is useless.

Only magically-warded locks should not be able to be opened by a mere Knock spell; Perhaps a Wish or Miracle will work.

we appear to be lacking wish and miracle, remember.

Fish we appear to be lacking wish and miracle, remember.