Follow The Steps -:
1) Open WhatsApp
2) Tap on any group chat
Tap and hold on your sent message, a menu will popup at the top of the screen. Tap on ‘i’ (information) symbol.
3) Now you can see a list of members who has read you message under ‘Read by’ section.
4) For those who haven’t read your message yet will be listed under ‘Delivered to’ section. That’s how to know who has read your WhatsApp Group Message on Android.