Question Detail

Generally, this problem occurs only when environmental variables are not configured properly. you can call keytool by specifying the full path to your Java/bin/keytool.exe file

for me, the path looks like this:
go on till here in your CMD
C:\Program Files\Java\jdk1.8.0_131\bin

and Fire your SHA1 Command.

If you are not able to find your debug.keystore file it should auto-generate when you create build APK in Android Studio by the way you can create it manually by follow below command in your CMD or terminal

keytool -genkey -v -keystore C:\Users\YOUR_PC_USER_NAME\.android\debug.keystore -storepass android -alias androiddebugkey -keypass android -dname "CN=Android Debug,O=Android,C=US"

How to get SHA 1 KEY in Mac or Linux

SHA-1 fingerprint of keystore certificate

Mac / linux OS Debug Fingerprint

keytool -list -v -keystore ~/.android/debug.keystore -alias androiddebugkey -storepass android -keypass android

for Release mode:

keytool -list -v -keystore {keystore_name} -alias {alias_name}

example:

keytool -list -v -keystore C:\FULL_PATH_TILL_ANDROID_KEYSTORE_FILE\KEYSTORE_NAME.jks -alias ALIAS_HERE