Where the Android-SDK is installed ？

Where the Android-SDK is installed depends on how you installed it.

If you downloaded the SDK through their website and then dragged/dropped the Application to your Applications folder, it's most likely here:
/Applications/ADT/sdk (as it is in your case).


If you installed the SDK using Homebrew (brew cask install android-sdk), then it's located here:
/usr/local/Caskroom/android-sdk/{YOUR_SDK_VERSION_NUMBER}


If the SDK was installed automatically as part of Android Studio then it's located here:
/Users/{YOUR_USER_NAME}/Library/Android/sdk


Once you know the location, open a terminal window and enter the following (changing out the path to the SDK to be however you installed it):
export ANDROID_HOME={YOUR_PATH}


Once you have this set, you need to add this to the PATH environment variable:
export PATH=$PATH:$ANDROID_HOME/tools:$ANDROID_HOME/platform-tools


Lastly apply these changes by re-sourcing .bash_profile:
source ~/.bash_profile