You can view read receipt's after a message has been sent by selecting "view recipients" in green, next to any sent message. Once a message is read, you will see two green ticks next to the recipients name.

See below for read receipt notice examples:

No time => Indicates that the user has not received this message yet

Only time => Indicates that the user has received the message but hasn't open it yet

Time + tick => Indicates that the user has received the message and has read it

0 ticks => Indicates that the user has not received the message yet

1 tick => Indicates that the user has received the message but hasn't opened it yet

2 ticks => Indicates that the user has received the message and has read it