First define a group of all your mesh points by setting the type filter to mesh point. Then create a second group and set the method to related nodes and select as input the group of mesh points. As a result you should get a group of nodes that are related to the mesh points.
Note that the intermediate group containing mesh points is not required. When the New Group dialog is open, set the Smart Selection Method (red outline in the image below) to "Related Nodes", then pick the mesh points.
Also note: if other visible entities (i.e. polygon faces or meshes) are taking precedence in the selector, you can also set the selection Type filter (yellow outline) to Mesh Points.