The memo field is not printed when using the "Print Check" feature.

The "Custom check format" dialog allows the user to change the position of
the nonexistent memo field.

Though the function (gnc:print-check payee amount date memo) in
print-check.scm takes a memo parameter, memo printing code within it is
conspicuously absent.

I tried adding the following code just to see what would happen:

      (let ((memo-pos (assq 'memo format)))
        (gnc:print-session-moveto ps (cadr memo-pos) 
                                  (+ offset (caddr memo-pos)))
        (gnc:print-session-text ps memo))

The result:  Sometimes it would print the memo, sometimes it would print
the wrong memo, and sometimes it wouldn't print anything.