How do I log into minecraft with my account username?
I had this same problem awhile back. Your best bet is to contact Mojang at their contact section and explain that you do not have access to the email that you originally signed up with (or in this case, explain that you don't know which email you used) . They will most likely ask you for proof of purchase associated with the account name. They can then set the email for your username to one that you would like.