Can you please elaborate it or give some sample records with final results that you want to achieve?
Make sure one thing your flag can have more values then you expressed in question.
Below query will work for you :
CASE WHEN Route_cd=Event_Actual_Dttm AND Event_Actual_Dttm=Src_Obj_Id THEN 0
WHEN Route_cd<>Src_Obj_Id AND Event_Actual_Dttm=Src_Obj_Id THEN 1
WHEN Route_cd=Src_Obj_Id AND Event_Actual_Dttm<>Src_Obj_Id THEN 2
END AS flag
FROM cktmpA A CROSS JOIN cktmpB B
ORDER BY flag