Hi Raja
You can create variant and make it default. Click on account assignment field, then press F2 button. Then select not equal to blank for cost center field.
The purpose of this report is look for purchasing documents that belong to some account assignment. but you can use other reports other than ME2K if you want to view all purchase orders such as ME2N, ME80FN, ME2L or ME2M. Each report have its own purpose.
For General analysis use ME80FN.
Thanks,
Jagdeep