If you decided to go with Triss, you'll be back inside the keep (M2.5) and Triss will give you the potion that enhances your energy regeneration rate. Thanks to it, you'll be able to use Aard more often. You don't have to drink it in order to beat Savolla. You can drink your Swallow potion, though. Go further to face Savolla (M2.6).
First kill 4 bandits who support Savolla's energy shield. Use strong fighting style against them.
The thing with Savolla is that he can teleport and use magic against you. Defeating him is based on preventing him from casting spells. When he disappears, carefully look around and quickly engage him with a strong style wherever he reappears. Now's a good time to check if you've caught the hang of combat system already. After defeating the wizard, don't forget to take the equipment from his body.
Run to Laboratory and to the stairs (M2.4). You'll see that Triss is hurt. You won't be able to help her for now.