While using Gnome Do, I discovered that man pages could also be opened in help window as shown in this image.
What is the command to open manuals in help through terminal?
gnome-helpis the application you are looking for. These are part of system document browser. You can open manual pages in different window (as shown in the image in your question) from terminal as,
For example, to get man page for
python in different window.
You can also open
info also using
yelp file:///usr/share/gnome/help/gcalctool/C/gcalctool.xml yelp info:make