Hi Makh Nath,
Let me try to understand what you’re after exactly :-)
Do you mean a version of Keyboard Viewer that shows only a numeric keypad, so you can enter numbers by clicking them with the mouse/trackpad?
With the standard Keyboard Viewer, you can already do that, only, all the numbers are on the top row – is that a problem?
The macOS Keyboard Viewer panel can be customized, so I guess you can make that into an onscreen numeric keypad.
But I can be of no help there, as I haven’t tried my hand on that.
Would an alternative be to bring up the calculator and type on that?
You can switch it to View > Show History, thereby making copying from it even easier.