Definition: sequence s = get_position()
Description: Return the current line and column position of the cursor as a 2-element sequence {line, column}.

Note that under Linux get_position() simply always returns {0,0}. I doubt it would be spectacularly difficult to maintain a couple of new variables in builtins\VM\pfileioN.e to keep track of the cursor position: fairly trivial for plain ascii, slightly trickier for embedded \r\n, but getting quite a bit thornier for embedded ncurses and unicode characters. It would probably be a safer bet for an application to maintain its own x,y internally, if at all possible.
pwa/p2js: Not supported
Implementation: via :%opGetPos / fget_position() in builtins\VM\pfileioN.e (an autoinclude).
See Also: position