(apropos "CLASS-SLOTS") reports CLOS:CLASS-SLOTS.

  (clos:class-slots <class>) yields a list of slot definitions for that
  class, such as (class-of *standard-output*).  CLOS::SLOTD-NAME returns
  the slot name of a slot definition.

(mapcar #'clos::slotd-name (clos:class-slots (class-of *standard-output*)))
=> (write-sequence read-sequence write-string write-char write-byte excl::read-char-nh read-char read-byte listen excl::external-format ...)

#:Erik