"너와의" => (of something) to do with you. - 너: you. - 너와: with you. 와 is a particle meaning "with" or "together with". - 너와의: 의 is a possessive particle, so it is "of, or relating to something to do with you". - 나는 너와 대화한다: I converse with you. - 너와 나의 대화: conversation between [of] you and me (a noun phrase). - 너와의 대화는 즐거웠다: My conversation with you was fun. * 너의 대화 would mean "your conversation". To make it "(my) conversation with you", we need 와 - "(나의) 너와의 대화".