Some or all of a Point Cloud or
Mesh’s triangles can be ‘split off’ and placed in a new
cloud/mesh. While in Cloud/Mesh Edit Mode (or Cloud/Mesh Edit Mode), select
points or triangles (shift select or use the temporary region select), then
click the Split Cloud/Mesh tool on the toolbar 
.
The selected points and triangles will be cut and placed into a new Point Cloud(s)/Mesh(es).
If you select points from multiple Point Clouds the selected points will be placed together into a single new Point Cloud.
If you select triangles while also selecting points from separate Meshes, the selected triangles will be cut and put into a new Mesh and the points will be put into a separate Point Cloud.