Information about how to defeat Golyat in The Witcher 3 Blood and Wine.
Golyat, provoked by a knight with more ardor than sense, will make quite an entrance, and fortunately for the knight who enraged Golyat, the spectacle will occur right in front of Geralt and his two escorts. Geralt, being a good Witcher (and something of a knight himself), naturally decides to intervene.
Golyat, despite his fearsome size, isn’t terribly powerful and possesses only four attacks: a quick swipe with his improvised club, an overhand smash with his cudgel (sometimes appending a charge), a spinning, three-rotation attack which he advertises well in advance, and a stomp, the force of which somehow he’s able to project in a cone in front of him.
All of these can be blocked and absorbed with Quen, as well as simply dodged. Hitting him with a strong attack before dodging his inevitable counter will suffice to whittle him down, and setting him on fire with Igni will do a bit of damage, as well. If you want to take him out more creatively, however, use your crossbow and aim at his eye, or rather, at the eye slit in the center-right of his barrel helmet (right from your perspective, not Golyat’s right). You don’t need to whittle the giant down or anything, one well-placed shot will fell the monster. Of course, considering the inherent inaccuracy of the crossbow and the fact that Golyat probably won’t deign to stand still while you aim, this will probably be more a matter of repetition and luck than one of accuracy and finesse.
If you’re inclined to fight Golyat conventionally, the tried and true strong attack followed by a backwards dodge works well against him. The iframes from dodging should allow you to avoid damage from most of Golyat’s attacks, and even on Death March! difficulty a late-game Geralt should be able to weather 3-4 attacks from Golyat, and a fully upgrade “Active Shield” Quen should ensure you’re never in any real danger of dying. Ogroid oil will enhance the damage you deal, while Igni, despite not stated as one of Golyat’s weaknesses, does a fine job of whittling down Golyat with its damage over time burn effect. After a bit of dodging and dancing with the odd sign thrown in to heal or burn, Golyat should fall.