He's a bit unpredictable when it comes to movement, but you'll be able to figure out where to hit it if you pay attention
When fighitng Shaelmaars, the best way to deal with them is to let them charge at you with their rolling attack and dodge it to let them hit the wall behind you leaving them toppled and very vulnerable to multiple attacks Quen helps protect Geralt, but a single hit can remove the protection Prepare Samum bombs and use Aard to attract the beast to the walls. Dodge and attack while the creature is stunned. Home Witcher 3 shaelmaar quest Shaelmaar Witcher Wiki Fando