How to view values using the "Viewer Node" in the Geometry nodes - Blender 3.1

 It's a bit tricky if you want to view or display a value using the Viewer Node because it simply won't work if you use a node setup as shown in the following picture:

The trick is that you need to connect something to the geometry input and you need to connect an object that has at least one vertex. You cannot connect an empty or something like that. The easiest way to do it is that you can select any node from the Mesh Primitives (e.g. Ico Sphere node) and connect it to the viewer node like that:

This way you will be able to see it in the Viewer column in the SpreadSheet and make sure that the Viewer Node option is chosen:

Instead of the "Ico Sphere" node, you can also use the "Object info" node or the "Group Input" node. Again, make sure that your object is non-empty. 

In my opinion, the way we can debug in Animation Nodes was great because we just plug any value to the viewer node and see the value in the node itself (The value is displayed on the node). I hope they improve the viewer node of Geometry Nodes in the future.