Gmail integration email sends and opens will appear in the contact's record under their Activity Feed. The activity will be noted with "via Gmail" at the end of the subject line.
Accessing the email subject line will open a modal box for a recap of the conversation and the included recipients.
Only the user of the sending email address can view the email content and recipients of Gmail integration activity. Clicking into the subject line of an email sent through another user's Gmail address will result in the following popup: