Well, first make sure you try any E-mail address you can recall ever having used.
If you can not under any circumstance find it (I say this because asking Z8games Support is a tedious and long process.) Then you must contact Z8games Support;
Z8Games - Support
In your ticket write the following;
Your situation: Unable to find my E-mail which inhibits me from finding my security answer to leave current clan.
Your IP Address:
Any Details you do remember from your sign up process:
I wish you luck, As i said this process is long, and usually frustrating, I hope you can find your E=mail and do a recovery instead. =/
It's best you write information like this down to prevent it from happening in the future.