I'm not quite clear on what you want to do, but if you're rooted and want root access in a terminal, do the following...
Install ADB on your pc.
https://developer.android.com/studio/releases/platform-tools.html
Enable ADB debugging in developer options of your phone.
Plug your phone to your pc.
Run the following command to see if adb recognizes your phone:
Enter your phone's shell ($):
Switch to a root shell (#):
Keep an eye on your phone after running this command. You may get a prompt requesting root access (grant it).
Once at the root shell, you can cd to wherever you wish to wreak havoc in your phone.
Example:
To go into the system directory you run this:
To list everything in system to see files or what directory you wish to go to next:
You can do all of the above from a terminal emulator app, but it's easier plugged to your pc. Be careful what you do. Don't want to end up bricked.