If your Helpshift SDK version is later than iOS v5.5.0 / Android v4.4.0, you have the ability to see when your users read their messages on their devices. These are known as Sent Receipts and Read Receipts. You will automatically see this info in your Issues view on the Dashboard.
Hovering over the timestamp with your mouse will display additional details about the message history.
Please note: You will not be able to see when Email/Web users read their messages, only SDK users.