My downstairs neighbor has a leak in her kitchen over her kitchen cabinets in the wall. My kitchen is made identical to hers. My question is if there is nothing wet around my sink or nothing leaking (everything is completely dry) even the cabinet under my sink is dry. Do I suggest to my Neighbor to open the wall to find out why there is water coming out of her wall?

Yes. The leak is probably in the ceiling. Open up the ceiling, you turn water ON in your place, go down, and see where the water is coming from.

Back to you / Milo

Milo's dead on! Before you can repair a leak you must first locate the source and it's my bet , after you open the ceiling you'll find the leak coming from your kitchen. Good luck, tom