I would never have pegged Cel as having time for pets, but here we are.
Your goal in this trial is to kill all ten orcs, with bonus objectives to kill four with sneak attacks from above, and kill all without being detected. Note that an orc discovering the dead bodies of his clanmates does not count as detection. Start by taking out the orc from atop the nearest tower. Your caragor can climb towers as easily as you can, but use Wraith Vision first to make sure that the enemy's back is turned.
Leap to the near platform to take out that archer as well.
You've now bought yourself some space- no other orcs can see you from atop the two vantages you've just cleared. This is a good spot to get your death-from-above kills. Use Wraith Vision to pick your targets, then advance to the edge and stealth kill as normal. Jump back up the platform and repeat
Once you've got your four requireds, kill the rest with regular stealth. Most will be pretty scattered at this point, but if you do find any too clumped together for comfort, remember that you can still fire a bow from the saddle.
Kill the last to compete the task.