With 1 molecule you could observe it adhering to a surface, which technically could be considered wet. If you had 2, then you could observe whether they tend to cohere more to each other or to something else. If I spray water on a vertical surface of wax, the wax does get wet. The water molecules have greater cohesion to each other, so they form beads rather than a film, but the beads definitely do adhere to wax due to intramolecular forces, which is wetness.
Also, wetness can be an intrinsic characteristic, it isn’t entirely relative to the contact surface. Water is considered to be “wetter” if soap is added to it, this is why fire trucks add surfactants to water used to fight fires (called a “loaded stream”).