"What date is it?"
几=question asking about the no. of the date. 几月几号？ 几(what)月(month)几(what)号(day)? In chinese, most of the inquisitive sentences (except the yes/no question-which you'd just add 吗 at the end) are likely to have the same sentence structure as the answer they are looking for, the question markers such as 什么，多少，几，哪，怎么，etc. Like this question, it could be answered: "七月四号“ = "July 4" 七月=July, 四号=4th day.