You can use a keyboard object to create notes with the mouse. A keyboard object also displays all notes passing through it. In this sense, you can think of it as a real-time, MIDI note on monitor. Although you can record the output of the keyboard in Logic Pro, its main purpose is for testing and monitoring in the Environment.
Choose New > Keyboard (or use the New Keyboard key command).
Apart from the Icon parameter, you can also set the following in the Object Parameter box: