Opening a new Finder *tab* from command line
You really can't via any “normal” shell commands, but you can run AppleScript via the shell to accomplish the task.

Here's a Bash function with the command fnt for “Finder New Tab”:

function fnt()
{
    osascript -e 'tell application "System Events" to perform action "AXPress" of menu item "New Tab" of menu "File" of menu bar item "File" of menu bar 1 of application process "Finder"'
}


Add the above bash function to your ~/.bash_profile or ̃/.profile file to use it. After adding, restart Terminal or use the source command in the current Terminal window to have access to the fnt function.

This should work on any version macOS that has the “New Tab” command in the “File” menu. You'll also need to add Terminal to: System Preferences > Security &amp; Privacy > Privacy Accessibility

I understand some improvement to AppleScript has been made in Mojave relative to tabs in the Finder, but I'm still using macOS Sierra 10.12.6 and can't test.