This page of IGN's Mass Effect wiki guide is all about the Scan the Keeper Side Quest on the Citadel, including where and how to find all 21 Keepers on the Citadel. There are multiple different ways ...

The first thing you may want to do is reset the printer scanner. This is a simple task, so we do not expect most users to find it too difficult. To reset the printer scanner, the user must power it ...