This isn't quite for displaying attributes, but it's still useful.
The Node Wrangler Add-on has a hotkey for connecting something to the output with a single click. Node Wrangler is one of the built-in add-ons, so if you go to Preferences > Add-ons > Community, it should already be there. Simply hit the check mark to enable it.
Alt+Shift+Left Click any node that has a Geometry output and it'll connect it to the output, so that you can see what that intermediate step looks like in the Viewport.
This doesn't work for values like float or int since they are not geometry, but you can just hover over the output or input socket of a node and it'll display the computed value in a tooltip.
If the tooltip says 'The socket value has not been computed yet.', you can Ctrl+Shift+Left Click that node to connect a Viewer Node (works without Node Wrangler), which will make the value show up in the Spreadsheet. The value will then be computed and hovering should work again (...if you have the spreadsheet open, and if it is set to Viewer Node)