Based on Adele's enjoyment of making sketches and creating characters and images in his journal, a drawing or painting class would likely best fit his interests. These mediums would allow him to further develop his skills in character design and illustration, which aligns with his passion for sketching.
If he is particularly interested in digital art, a class that focuses on digital drawing techniques could also be beneficial. Alternatively, if he wants to explore three-dimensional aspects of his creativity, a sculpture class could provide an exciting new avenue. Ultimately, a drawing or painting class would likely be the most aligned with his background and interests.