Using the normal tool , to select a group as a whole, click on any part of the grouped objects.

Notes

When you select more objects, being them grouped or not, large selection handles appear around group, and tiny handles appear around each object.

At this point it is not possible distinguish a group from multiple selection - the only safe test is to click over selection again: if the handles displacement remains the same, it means it is a group; if it turns into a single selection, it was a multiple selection, not a group.