Sometimes XQuartz windows go somewhere off the screen if you are using multiple monitors.
To bring back the window, you may be able to use wmctrl utility which
can be installed as, :
$ brew install wmctrl
And you can see XQuartz window list as, :
$ wmctrl -G -l
0x00600008 0 0 44 200 200 N/A Gnuplot
It seems the window I am now looking for is at the position (0,0) with width and height (200,200), but it is not seen on the screen. Try something like, :
$ wmctrl -i -r 0x00600008 -e 0,200,2000,200,200
which means specify windows in number -i -r 0x00600008, and specify
the position (x,y), and width and height (w,h) as -e 0,x,y,w,h.
It seems that the position (x,y) is not correctly pointing the up and left corner, so we need to specify some large values for (x,y), in this case (200,2000), but I don’t know what is the apropriate values for the coordinate, though. At least, I could bring back my window from outside the screen.