The best area to complete Sight of Surrender bestiary is in the Dark Grounds by Roshamuul depot. The Dark Grounds can be opened when the server has completed 20 Soothing Bad Dreams task. More information on this can be found here. Once that has been completed the Dark Grounds will open for 20-25 days starting at the following server save.
The entrance to the spawn can be found here:

The best way to finish the bestiary would be during Rapid Respawn when a large team is hunting here. All you have to do is hit them once for them to count in your bestiary. During the event you can sometimes find 10-20 people at a time doing these which will make them go quickly.
Outside of the event the most efficient way is to have either a Knight or Paladin that will be blocking them and having enough shooters to kill them quickly as they have a lot of health.
Sources:
www.tibiaqa.com/7841/how-to-open-sight-arena-dark-grounds-located-north-of-roshamuul-depot#a23770
https://www.tibiaqa.com/22123/exactly-where-is-the-entrance-to-dark-grounds?show=22123#q22123