Command to open new terminal window from the current terminal?

Just this command will do:

gnome-terminal

Normally if you want a command to open from the terminal and separate (so it returns to the prompt without having to close the opened program), you have to use something like this:

gnome-terminal & disown

However the parent terminal seems to detect that the same command is being used so you don't need to do that and gnome-terminal will suffice. This also seems to happen when running xfce4-terminal from Xfce's terminal, konsole from KDE's as well (doesn't seem to work when running xterm from xterm (see also xterm xterm) - Running konsole from Gnome/Unity & Xfce's terminal works as well, but for Xfce's terminal in gnome terminal you need xfce4-terminal & disown).

For more visit gnome-terminal's manual page:

 gnome-terminal  [-e,  --command=STRING]   [-x, --execute ]  [--window-with-profile=PROFILENAME]  [--tab-with-profile=PRO‐
       FILENAME]    [--window-with-profile-internal-id=PROFILEID]    [--tab-with-profile-internal-id=PROFILEID]    [--role=ROLE]
       [--show-menubar]   [--hide-menubar]   [--geometry=GEOMETRY]   [--disable-factory]  [-t, --title=TITLE]  [--working-direc‐
       tory=DIRNAME]  [--usage]  [-?, --help]

Command to open new terminal window from the current terminal,

xdotool key ctrl+shift+n

To install xdotool,

sudo apt-get install xdotool