Hello 엘리자베스. 1st. please can you explain 인지 here. we use 인지 when we express a vague doubt or when we ask a question. examples) 이게 무슨 뜻인지 모르겠어. (I don't) know what this means. 이게 무슨 뜻인지 알아요? (Do you) know what this means? 꿈인지 생신지 모르겠어. I don't whether it's a dream or a reality. 2nd What is the diffarance between saying 무슨 and 몇 as what? Would it also be correct to say 오늘이 몇 날인지 알아 ? 무슨 is used for asking about something's characteristic. 몇 is used for numbers. you can find the difference in the following conversation. 오늘이 무슨 날인지 알아? do you know what day today is? 응. 오늘은 내 생일이야. yes. today is my birthday. 오늘이 며칠(며칠=몇+일, you can't say 몇 날)인지 알아? do you know what day today is? 응. 오늘은 14일이야. yes. today is 14th. 3: What is the diffarance between 날 and 요일 'day' ? Can you also say 오늘이 무슨 요일인지 알아 ? 요일 means a day of the week and 날 can mean 'a day', 'a date', 'days/time'. 오늘이 무슨 요일인지 알아 ? is correct :)