I want to open up my other Facebook account but I can't remember what email I used for it. It's been about 5 years ago I don't remember. How can I recover it ?
If you don't remember what email it used ... you probably can't "recover" it.
You could TRY logging in with all your past emails, if you think you know what password you used. But I'm guessing you have no idea what the password was, if you don't remember what the email was.
You could also TRY contacting Facebook - but they'd probably ask what your email was. And I think they now have a policy against having multiple accounts.