Various job lots seen to incorporate constant warning (6,6)
I believe the answer is:
object lesson
'warning' is the definition.
(object lesson is a kind of warning)
'various job lots seen to incorporate constant' is the wordplay.
'various' indicates anagramming the letters.
'to incorporate' means one lot of letters goes inside another.
'constant' becomes 'c' (mathematical abbreviation).
'job'+'lots'+'seen'='joblotsseen'
'joblotsseen' is an anagram of 'objetlesson'.
'objetlesson' going around 'c' is 'OBJECT LESSON'.
(Other definitions for object lesson that I've seen before include "Instructive experience" , "Example typifying a principle" , "What may be striking" , "punishment intended as a warning to others?" , "shows what one should do" .)