There are many correct answers.

Scheme defines some convenience functions for you. One of them is cadr, defined by 

  (define (cadr L) (car (cdr L)))
That is, the cadr (pronounced "cadder") of L is the second member of list L.

Here is a definition of descending. 

  (define (descending L)
    (cond
       ((null? L)        #t)
       ((null? (cdr L))  #t)
       ((> (car L) (cadr L)) (descending (cdr L)))
       (else             #f)
    )
  )