Check marks are displayed next to each message you send. Here’s what each one indicates:
In a group chat, the second check mark will appear when all participants in the group have received your message. Two blue check marks will appear when all participants in the group have read your message.
For any message that you send, you’ll be able to see a message info screen, displaying the details of when your message was delivered, read, or played by the recipient. When a participant leaves a group, the message info screen will still show the original information with all participants, including the participant who left the group.
To see the message info screen:
The Message Info screen shows:
If you don't see two blue check marks next to your sent message:
You can disable read receipts for individual chats. This won't disable the read receipts for group chats or play receipts for voice messages. There's no way to turn those settings off.