It depends on your personal preference. If you prefer visual storytelling and action - packed scenes right from the start, the manga is a great choice. The manga's art is stunning and it can quickly draw you into the story with its exciting battles and cool character designs. However, if you like to really get into the details of the story, the characters' thoughts, and a more in - depth exploration of the world, then the novel might be better for you. The novel has more room to develop the story and can provide a more comprehensive view of the Solo Leveling universe.
You can start from the chapter where the anime ended. Usually, there are online forums or manga communities that can give you the exact chapter number.