It's very simple follow below steps.

Step 1. Go to your project directory in VS code or Android Studio.
Step 2. Open terminal.
Step 3. Run cd android for the below path :
Ex.: PS D:\Workspace\FlutterWorkSpace\FlutterApp\flutter_demo_app> cd android
Step 4. Run .\gradlew signingReport for the below path :

PS D:\Workspace\FlutterWorkSpace\FlutterApp\flutter_demo_app\android> .\gradlew signingReport

Then it will display like that:

> Task :app:signingReport
Variant: debug
Config: debug
Store: C:\Users\User\.android\debug.keystore
Alias: AndroidDebugKey
MD5: 6C:64:D6:49:31:37:60:3F:1D:2E:31:2A:F4:3C:E3:D6
SHA1: 54:B0:BC:D6:D6:B4:C3:51:88:E9:20:62:56:CD:23:2D:A7:C0:0F:FD
SHA-256: 80:BF:B3:A8:0D:D6:D9:7C:C8:5F:61:32:22:6B:EA:D1:51:03:8D:1H:5E:0F:F7:0B:G3:56:1DD1:D1:3B:DB:FA
Valid until: Monday, 30 March, 2048

Credit:  BloodyMery