In your project directory you will find a
Proguard folder, in which you will see four text files:
Describes the internal structure of all the class files in the .apk file
Lists the mapping between the original and obfuscated class, method, and field names. This file is important when you receive a bug report from
a release build, because it translates the obfuscated stack trace back to the
original class, method, and member names. See Decoding Obfuscated Stack Traces
for more information.
Lists the classes and members that are not obfuscated
Lists the code that was stripped from the .apk
Hope this helps!
Here is probably a more visual way to check.
In the newer release of Android Studio, it comes with the APK Analyser that let user explore what is in the APK file and it is handy to check if your class has been obfuscated.
Below image shows that both package and method name have been obfuscated