Taken from real life walks on the red carpet for gala events. Prominent attendees are asked Who Are You Wearing? This refers to a specific fashion designer of a dress or any outfit that person maybe wearing.
In the metaverse world (decentraland, sandbox, etc.) articles of clothing are called wearables. So when asking Who Are You Wearable, you are asking or being asked who designed your avatars clothes. This can include shoes, jewelry, body parts such as eyes or hair, hats, and many other accessories. Knowing who designed the item gives designers exposure and others can then search for their collection in a NFT marketplace.
Person #1: Hey, I love that look. Who are you wearable?
Person #2: Thanks. I got it from Goldi Lox. She has some great wearables. You should see her collection.
(Goldi Lox is an actual wearable designer. You can find her wearables in the decentraland marketplace)