Electrical plug at bathroom sink, can it be located in a cabinet next to bathroom sink?
No, the receptacle within an adjacent cabinet does not satisfy the code requirement.


  210.52(D) - Bathrooms.
  
  In dwelling units, at least one receptacle outlet shall be installed
  in bathrooms within (3 ft) of the outside edge of each basin. The
  receptacle outlet shall be located on a wall or partition that is
  adjacent to the basin or basin countertop, located on the countertop,
  or installed on the side or face of the basin cabinet. In no case
  shall the receptacle be located more than (12 in.) below the top of
  the basin.





  210.52 - Dwelling Unit Receptacle Outlets
  
  The receptacles required by this section shall be in addition to any
  receptacle that is:
  
  (3) Located within cabinets or cupboards