Where are you from?
Are you appearing for certification exam?
You will find lot of Practice questions or Interview question papers on net if you search on Google.
There are also many sites where you will be able to practice online test papers. (May be paid sites)
You can find my email ID and contact detail on my SCN profile.
Mail me out of the SCN and I will share as much of material is available with me.
I don't think you will find any such source where you can answer sample questions.- Unlike other technologies you wont find dumps online for SAP. You have to refer and work personally. SAP has its own standards and one must always go by SAP reference guide.
Hope this answers your query.
you can purchase the professional SAP Certification preparation package by contacting your local SAP office. It contains all relevant materials plus exam voucher to pass the exam successfully: https://training.sap.com
Hope it helps and good luck with your exam,