Failed to fetch https://osquery-packages.s3.amazonaws.com/xenial/dists/xenial /main/binary-amd64/Packages 404 Not Found Can anyone guide how can we resolve this..in ubuntu 16.04

I think that’s an old URL. You might want to follow the instructions on the bottom of this page https://www.osquery.io/downloads/official/5.0.1, in the Debian Linux tab.

What Stefano said. osquery is static, and we no longer maintain release specific repos.