Hey there!
Fortunately in many cases although unfortunate in your specific case, Mojang, the company who makes the game, does not provide any way for server operators to get any information like that.
You could try email/password combinations that might be the ones you used when creating that account here:
https://account.mojang.com/loginOn that page I linked, there's also a place to reset the account's password if you think you know the email but have no idea what the account password might be. If you're not sure on the email you used, you'd have to talk to Mojang support directly but they might be able to help you out if you had the original payment transaction ID from when you bought the account, plus the account's Minecraft name.
Good luck!