Hay is for horses. You grew up on a farm?
plot (with hoc language from terminal or GUI of NEURON) the input signal of the current I am injecting with a PointProcessManager
Actually, the PointProcessManager isn't injecting any current. What's injecting current is an instance of a point process class that is managed by the PointProcessManager.
The PointProcessManager's "parameters" page will show the name of the object class and its instance. This will be of the form
will be something like IClamp, SEClamp, or AlphaSynapse, and index
will be a nonnegative whole number (0, 1, 2 etc.). Also on that page check the buttons below the object instance name to discover what the point process's current is called (you'll probably see a button labeled i (nA)
Next bring up a graph by clicking on NEURON Main Menu / Graph / Current axis
and use its Plot what?
tool to enter the fully qualified name of the variable that you want the graph to plot; assuming that the current is called i, the fully qualified name will be of the form
Finally dismiss the Plot what?
tool by clicking on its "Accept" button.
For more information see the entry How do I plot something other than membrane potential?
in the FAQ list https://neuron.yale.edu/neuron/faq/general-questions