It is actually "VERB + -ㄴ 줄 알다". In your example, the verb is the special verb 이다(is), so 카드이(다) + -ㄴ 줄 아네. -ㄴ 줄(을/로) 알다 is similar to -ㄴ 것(을/으로) 알다, which means (mis)take a thing or a situation for something else. 줄 알다 is specialized for this usage, while 것을/것으로 알다 is more general, so 줄 알다 sounds more natural. -ㄴ 줄을 알다 indicates identifying or knowing something correctly, while -ㄴ 줄로 알다 is used for mistaken identification. In real life, we most often say -ㄴ 줄 알다 without the particle however, which can mean either of the two cases. But this ambiguity only occurs in isolated sentences, as the context and the intonation make it clear which is meant. Your sentence can be more clearly written like this. - 요즘 은행 가면 엄마 카드인 줄 아네 = 요즘 은행(에) 가면 (은행 사람들이) 내 카드가 엄마 카드인 줄 아네. = [요즘 은행(에) 가면] [(은행 사람들이) 내 카드가 엄마 카드인 줄] 아네. = [At the bank,] they know/think [that my card is actually my mother's]. Other examples: 1. 난 네가 영희에게 관심 있는 줄 알고 있었어 = I already knew you were interested in 영희. 2. 난 네가 화나서 그랬는 줄 알았어 = I thought you acted that way because you were angry. Again, -ㄴ 줄 알다 can be used for identifying something both correctly(1 - 줄을) and mistakenly(2 - 줄로).