How do I do a v look up between two different spread sheets?

This column has 3 responses , accept , decline or did not respond. I Need to do a v look up between two different spreadsheets of different days that gives the output of people that did not respond to the email in spreadsheet 1 , who have now responded the following day in either accepting or declining in the spreadsheet 2, how would I do a v look up to find this ?