Earrings for my brother’s graduation

Don't use the graduation as a reason to completely reinvent his style. An expensive pair can still sit in the box if it's much larger or brighter than anything he normally wears. Pay attention to the earrings he already chooses, especially their color, shape, and size. If his usual studs are small and sit close to the ear, keep roughly the same proportions and spend the money on a better stone and metal. The gift will feel like a real upgrade without looking unlike him.

Diamond studs would work well for this because they're valuable enough for a major graduation gift but still easy to wear after the ceremony. A clean shape in gold will look just as natural with a suit at his first professional job as it does with his regular clothes. You can look through men's stud earrings here https://pierrejewellery.com/katalog/earrings/studs/men-stud-earrings. If his style is darker and understated, a small black diamond in white gold could suit him better than a bright white stone. If he likes a little more shine, classic round diamond studs would be the safer choice. Compare the measurements with a pair he already owns so the new earrings feel like an upgrade without looking oversized.