To launch Android Emulator using MacOS Terminal follow below steps:
Step 1: Open Terminal and navigate to your sdk folder. if you are not sure about PATH of sdk you can check in your .bash_profile. It might be similar to one mentioned below.
$ cd /Users/tarungoswami/Library/Android/sdk
Step 2: Open emulator folder
Step 3: Type below command to launch
$ emulator -avd NameOfEmulator
If you are not sure about Name of emulator you can open Android Studio AVD Manager and check for Name in existing listed devices.