"Activation Lock for iPhone, iPad, and iPod touch" is a security feature with an added aspect of possibly deterring re-selling of stolen devices. To learn more click here --> http://support.apple.com/HT201365
For an individual to remove an activation lock this absolutely requires the information for the account that applied the lock. Click on this link to learn 'How to remove Activation Lock' --> https://support.apple.com/HT201441
If you do not know the required information and you are not the original owner, get the owner of the account to remove the lock or return the device for a refund or recycle it. The device is otherwise useless to you. If the owner is unknown and has not provided contact information as a message showing in the login screen, there is no way to contact the owner unless the person who gave you the device knows them.
For help dealing with lost Apple ID or password:
• "If you forgot your Apple ID" [this is likely an email address you are using or used in the past] click here --> https://support.apple.com/HT201354
• "If you forgot your Apple ID password" click here --> https://support.apple.com/HT201487
Apple can completely reset a device if a person can provide sufficient evidence of valid ownership. Do this online at: Activation Lock support request - https://al-support.apple.com/#/additional-support Apple says, "Proof of ownership documentation is required," but does not state what currently constitutes proof. Prior to this new online service Apple typically required the original receipt issued by an Apple Authorized dealer and documented provenance (so typically it would be the original owner who does this, or a descendant with legal proof of ownership).
I'll add that dealing with forgotten security questions is pretty much its own issue. "If you forgot the answers to your Apple ID security questions" click here --> https://support.apple.com/HT201485
If you see the message "not sufficient information", read this link:
Security and your Apple ID - https://support.apple.com/HT201303
"Without proof of your identity ... and other carefully selected criteria(1), Apple Support can't help you perform any actions on your account." If you are still using security questions (see below) then you knowing your security question answers is the exclusive way, apart from potentially "other carefully selected criteria", of proving to Apple that you are the owner of that account.
(1) E.g., "In certain cases, Apple might also use your payment information to help verify your identity.You might need to verify your payment information to reset your Apple ID password" - https://support.apple.com/HT208683
Apple does have "Account Recovery when you can’t reset your Apple ID password" ( https://support.apple.com/HT204921 ) which it specifies is available for "when you don’t have enough information to reset your password." However, it also states it is "if you use two-factor authentication" which you may not be if you are still using security questions. You can investigate if this is even available to you.
It may ultimately prove very difficult to find satisfactory resolution to forgotten security questions if you get the "not sufficient information" message (e.g., https://discussions.apple.com/thread/252410816 ). For quite some time now Apple has been very strongly urging users to use Two Factor Authentication instead of security questions. --> https://support.apple.com/HT204915 "With two-factor authentication, you don't need to remember any security questions. We verify your identity exclusively using your password and verification codes sent to your trusted devices and phone numbers. When you enroll in two-factor authentication, we keep your old security questions on file for two weeks in case you need to return your account to its previous security settings. After that, they're deleted."
With that in consideration you can try to "Contact Apple for help with Apple ID account security". Click here --> https://support.apple.com/HT204169 If the online option does not resolve the problem I suggest trying to get a personalized response with a chat or telephone call. To talk by telephone: Contact Apple for support and service - Apple Support --> https://support.apple.com/HT201232
For other support options including those if your country does not have telephone support: https://support.apple.com/choose-country-region To chat, choose any topic, (not Apple ID) continue working your way down options until you find one with chat support, then ask to be redirected.
(Note: If your country is not listed, there may be a support option at the end of each region section for "other".)