Which 2006 Cobra Starship song has work done of guest vocals?
CREATE TABLE "guest_appearances" (
  "year" real,
  "song" text,
  "work_done" text,
  "artist_s" text,
  "album" text
);
SELECT "song" FROM "guest_appearances" WHERE "work_done"='guest vocals' AND "year"=2006 AND "artist_s"='cobra starship';