The Senators and all NHL franchises have scouts that live in various locations around North America, and they attend College games, AHL games, Junior games and any other games available for them in their particular scouting area assigned to them.
For example, a Scout living in Wilkes Barre PA probably attends games there, Birmingham, Hersey and Allentown which all have AHL franchises stocked with Prospects from four NHL teams, plus the visiting team's prospects.
Where else, besides the minor leagues would you expect drafted NHL prospects to be playing, besides Junior?
This is a common operating procedures and common knowledge.