Hi @Sushma G Muttalli ,

You can export XML for all records in a table.  Navigate to the list of records you want to export.  For example, type 'kb_knowledge.LIST' in the filter navigator box to open all of the kb_knowledge records in a new tab.  Filter, if needed, to show only the articles you want to export.  Export > XML as normal.  It will export all of those records.  Go to your target instance, from any list view (doesn't have to be kb_knowledge records, but easier to verify import if you are there), select "Import XML" from the menu option.  

As far as Import Set table, you are creating the staging table, which will be a custom table.  After you create the import set, you will create the Data Source and Transform Map. The transform map is where you will map from your custom staging table (u_kb_knowledge) to the actual ServiceNow table (kb_knowledge).

Mark my answer correct & Helpful, if Applicable.

Thanks,
Sandeep