What event was the opponent Karl Knothe and had a submission (rear naked choke)?
CREATE TABLE "mixed_martial_arts_record" (
  "res" text,
  "record" text,
  "opponent" text,
  "method" text,
  "event" text,
  "round" text
);
SELECT "event" FROM "mixed_martial_arts_record" WHERE "method"='submission (rear naked choke)' AND "opponent"='karl knothe';