What is the team 2 for the match with a team 1 of Panathinaikos?
CREATE TABLE "round_of_16" (
  "team_1" text,
  "agg" text,
  "team_2" text,
  "1st_leg" text,
  "2nd_leg" text
);
SELECT "team_2" FROM "round_of_16" WHERE "team_1"='panathinaikos';