Handwriting, by definition, is joined lettering. Printing has separate letters.
So "joined" is not needed to describe "handwriting".
But eliminating the word "joined" does present a problem with what you mean by the sentence
I donít know and don't understand handwriting.
The reader wonders..."Does he not recognize the words when they are written or is it the actual making the words that is the problem?"....or is it both?
Student or Learner