open the trunk with the key in the lock then with the trunk open remove the key from the lock then close the trunk.Give it a good squirt of penetrant while its open .
I know what he said but maybe the trunk adjustment is off or too tight and the tension is holding the key.Stranger things have happened,couldn't hurt to try and if that don't work he could remove it and work on it.he said that the key is stuck.. won't come out...
i'd pop the cylinder out and then figure out what to do.. if nothing else, take it to a locksmith...