This trophy is story-related and cannot be missed via normal campaign progression.
You will have two targets to eliminate by the end of this sequence. Both targets, Dante and Silvio, will be killed at the same time. You will fight Dante once without Silvio in the mix. You cannot kill Dante but you must wound him enough to make him retreat.
When you meet your two targets again, you must give chase through the port area of Venice. You are able to kill each target one at a time, but it is completely possible to kill both with one attack (you must have your double hidden blades equipped for this though).