On each occasion you defeat an enemy for the first time, you’ll be able to instruct BD-1 to scan them by pressing down on the d-pad when prompted. During the course of the story, you’ll be able to complete the majority of the Tactical Guide, but you’ll also need to complete Bounties for Caij, as each class of Haxion Brood also counts towards this. Same goes for legendary adversaries - you’ll have to scan some of those, too.