Emoji: button to the left of text box!
Web interface: https://web.whatsapp.com/ App menu does not have the button for me: http://android.stackexchange.com/questions/96531/how-to-scan-qr-code-for-whatsapp-web#comment162747_96547
Double ticks: https://www.quora.com/Do-double-grey-ticks-on-the-WhatsApp-mean-the-person-is-online
- 1 gray tick: sent to server
- 2 gray ticks: sent to recipient's phone
- 2 blue ticks: recipient read the message
Messages only kept in the server for a limited amount of time until delivered: https://www.howdoesappingwork.com/whatsapp/how-does-it-work/does-whatsapp-save-my-messages-on-their-servers/
And now with end to end encryption, you have even less chances of retrieving data from the server.