Although you cannot 'Do It' directly on an argument of a procedure, event, or local variable, you can still view their values.
Create one or more global variables for each of the arguments or local variables.
Then inside the procedure or event blocks assign the value of the arguments or local variables to the global variables.
Place a getter block for the global variables outside the procedure on the Blocks Canvas.
You can then test your app with the emulator or Companion app and device then check the values of the global variables with 'Do It'.
For procedures, you can also test by using 'Do It' directly on a call block to the procedure itself that you have dragged out onto the Blocks Canvas.
Fill in any arguments with test values.
Then right-click and 'Do It' on the procedure call block.
If the procedure returns a value, the value will display, otherwise the global variable's value is now set and can be viewed with 'Do It'.