The idea is the same no matter which side of the object you're trying to photograph: to eliminate shadows, use soft light from all directions.

You achieve that with large, diffuse light sources. In your example, these sources were the white walls of the light box, which bounce light all around the inside of the box. Another way is to build a box with open sides and cover it with translucent white material (fabric, paper, etc.) that you can light from outside the box.

None of that changes when you're shooting a top view. In fact, if you read to the end of the article you linked, there's a sample top view of a necklace that was taken by shooting through a hole in the top of the box. For taller objects, construct a somewhat deeper box, place it on its back so that the open side is facing up, and shoot downward.

Another option is to use a ring light or a ring flash adapter. These both attach to your camera lens and emit light from all sides of the lens, minimizing shadows. True ring flashes can be expensive (e.g. Canon's offering costs around $500) but offer the most power. Third party LED-based versions are much less expensive but provide much less light, and may or may not be suitable for your use. Ring adapters are essentially ring-shaped reflectors that distribute light from a regular speedlight; they're an inexpensive option, but more awkward to use than the real thing.