This guide is for those whom cannot complete the quest "A sighting" due to a bug.
The bug occurs upon entering the cave at the beginning of the side mission, there is no triggered cutscene. Instead the player faces a bugged out Brûz who will not do anything but stand in place and there is no progression in the mission, making it unable to complete.
There are two solutions to fixing this particular problem. One for those who have not yet completed the game 100% and still have other side/main missions to complete. The second solution is for those who like myself have completed the game 100% everything done except for the bugged quest.
Solution 1: If incomplete, doing other side missions or main story missions will result in a fix. More specifically completing side quest in the Elatriel line will result in a fix such as the mission "Fire and Fury" once completing this mission you can run straight over and be able to complete "A Sighting" bug free.
Solution 2: If all other side/main missions are completed and you're stuck with nothing but a bugged out "A Sighting" mission, then simply run over to your fortress in Seregost (Same region where the quest is located) and partake in a fortress defense that you will want to lose. When you have lost your fortress run over to the side quest and the problem should be fixed. If you have no control over the fortress in the first place try taking the fortress and losing it again.