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You can create a Smart List and apply the "Sent Forward to a Friend Email" filter and another with the "Received Forward to a Friend Email" filter, then associate the parameter of the specific email you are looking to track. I am not sure if you can actually track it one for one (who sent the email to who) but this will at least let you see who did it and who got it. If you want to delve deeper, it should show up in the lead's activity log.
You can find more info here: 'Forward to a Friend Link' in Emails - Marketo Docs - Product Docs