The function nearest_neighbors is the function template version of the k nearest neighbors search on Delaunay triangulations. There are two versions of this function, one taking a point of the Delanay triangulation and the other taking a vertex handle.
#include <CGAL/nearest_neighbor_delaunay_2.h>
 

 
computes the $$k nearest neighbors of $$p in $$delau, and places the handles to the corresponding vertices as a sequence of objects of type Vertex_handle in a container of value type of $$res which points to the first object in the sequence. The function returns an output iterator pointing to the position beyond the end of the sequence. 
 

 
computes the $$k nearest neighbors of $$v (including $$v) in $$delau, and places them as a sequence of objects of type Vertex_handle in a container of value type of $$res which points to the first object in the sequence. The function returns an output iterator pointing to the position beyond the end of the sequence. 