any way to find out my nexon ID?

Well, recently, I've charged a Karma Coin code and it's said something along the lines of "You're charging to the account [Nexon ID]" with the confirmation, though that might just be because I logged in using my Nexon ID rather than the email.

Ahh, nope, just logged in with my email and it still says my Nexon ID.

You can do Purchase NX -> PayByCash, then select and amount and it should say:

NX Cash will be charged to your account: [Nexon ID]

It even works on the account where I had my Nexon ID deactivated in favor of the account email. And if you do it on an account which is only identified by an email, it'll give you a string of letters and numbers which I believe is also your Nexon ID, it's just generated now instead of user-defined.