How to Activate ipod touch? without username and password?

What iOS version is on the Touch? If it is iOS 7 you MUST have the Apple ID and password or the Activation Lock, an anti-theft protection, will lock you out, and that cannot be bypassed.

If it is not iOS 7 but is locked due to a passcode, you have to restore via recovery mode described in http://support.apple.com/kb/HT1212

If it is iOS 7 and he has Find My turned on, then there is o way around it except for him to login to his iCloud account and remove the Touch from his devices. That would let you restore it. There is no way to bypass the Activation Lock, including Apple.

Is there a way to find my Apple ID Name if I can't remember it?

Yes. Visit My Apple ID and click Find your Apple ID. See Finding your Apple ID if you'd like more information.

How do I change or recover a forgotten Apple ID Password?

If you've forgotten your Apple ID Password or want to change it, go to My Apple ID and follow the instructions. SeeChanging your Apple ID password if you'd like more information.

If your brother is the original purchaser and purchased it directly from Apple, Apple might be able to help

Contact iTunes

thats also my problem i dont know what apple i.d used in my ipod . i dont know what they used i.d to the activation of the ipod . is there any chance to use any apple i.d to activate my ipod ?

Is there a way to find my Apple ID Name if I can't remember it?

Yes. Visit My Apple ID and click Find your Apple ID. See Finding your Apple ID if you'd like more information.

How do I change or recover a forgotten Apple ID Password?

If you've forgotten your Apple ID Password or want to change it, go to My Apple ID and follow the instructions. See Changing your Apple ID password if you'd like more information.

If you purchased it from Apple and have proof of purchase contact Apple:

http://www.apple.com/support/itunes/contact/