Lsb_Release Command Not Found

Some reason you're missing that executable. I have it on mine and according to dpkg -S, it is part of the lsb-release package.

ned@flanders:~$ dpkg -S `which lsb_release`
lsb-release: /usr/bin/lsb_release

What does your system say about that package?

ned@flanders:~$ apt-cache policy lsb-release    
lsb-release:
  Installed: 4.0-0ubuntu20.3
  Candidate: 4.0-0ubuntu20.3
  Version table:
 *** 4.0-0ubuntu20.3 0
        500  precise-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     4.0-0ubuntu20 0
        500  precise/main amd64 Packages
ned@flanders:~$ 

You can install with sudo apt-get install lsb-release provided your apt sources are correct.

sudo apt-add-repository “deb $(lsb_release -sc) partner”

lsb_release-sc: command not found

I suspect that you simply forgot to put a whitespace between the command (lsb_release) and its options/switches (-sc).

Possible solution:

You are using the non-std apt-add- (should not matter), but are also using Windows-type unique characters for 'open-quote' and 'close quote'.

Try this instead:

sudo add-apt-repository "deb  $(lsb_release -sc) partner"