I've heard that it should be in the output but it's not there. It just has material output. I've enabled node wrangler which I've read should make the viewer node visible.
The viewer node is actually an Emission BSDF with its label changed to "Viewer." ShiftCtrlLMB on any node with an output and the the first output will be connected to the color input of "Viewer." Successive clicks will cycle through all the outputs of the desired node. Also note that if your scene exposure is changed, the viewer's strength will automatically adjust to compensate, but it will not compensate for changes to gamma.