For technical and also ethical reasons (it could be classed as spying), Mailtrack does not specifically tell you when your emails have been forwarded, and to whom they have been forwarded.
If an unusually high number of opens are being generated for a particular email that you've sent, however, then you can normally assume that the email has been forwarded.
When your emails are forwarded to someone else and that person opens the forwarded mail/downloads the tracking pixel you will receive an open notification. However, this open will be attributed to the original mail recipient as Mailtrack cannot technically (and legally) track forwarded emails, meaning it cannot identify that it was not the original recipient that opened the mail.