You probably need to explain in more detail how to do that…
You can’t just use the mentioned .ExecuteJavaScript in a WebButton.Pressed or a WebCanvas.Pressed - that doesn’t work (for me).
See also this Forum Thread: Copy Web To Clipboard with some more information about why this doesn’t work.
This only seems to work when you’re using the Web SDK, such as in @Ricardo_Cruz 's example: GitHub: piradoiv/xojo-web-cell-renderers (-> see TextWithCopyButtonCellRenderer).