Table schema:
CREATE TABLE table_13642023_2 (circuit VARCHAR, rnd VARCHAR, gtu_winning_team VARCHAR)

Question: On what circuit was the GTU winning team #59 Brumos Porsche - Audi in round 5? 
SQL: SELECT circuit FROM table_13642023_2 WHERE rnd = 5 AND gtu_winning_team = "#59 Brumos Porsche - Audi"