have two possible ways to get the internal function code for an SAP pushbutton:
Click the button with the mouse, but do not release the mouse button (this would
immediately invoke the function). Instead, press F1 now while holding the mouse
button down. The SAP system will then display a small window that contains the
internal function code.
Activate "Input Recording" in the GuiXT window. Click the button.
Display the recorded InputScript, it now contains the internal function code.