When using the Nested Analysis Output Node, you need to perform a bit of setup in the nested analysis before you can configure the node.
First, the nested analysis needs a "Placeholder Input" Node at the beginning. This node is what grabs the output data from the Nested Analysis Output Node. You'll need to set up the Input Pins for the fields it will be grabbing; the data names don't need to match exactly, but the data types do.
Then, it needs to end at an "output". This can be at a Custom Completion Status node, an Output Data Flow Node, etc...
Once this is done, you can then create the Nested Analysis Output Node in the original analysis. Select the nested analysis to read, then set up your Output Pins by matching the output pin fields up with the placeholder input fields.