JSM copy product data doesn't copy Assets from one site to another. 

Add support for copying
1. Asset object type custom fields
2. Assets linked to issues
3. Asset information and fields in forms linked to issues
4. Asset objects and schemas

Workarounds

• 3rd-party apps can be leveraged to perform this migration.  For example: Community Post: 3rd-party Assets Migration
• Objects can be exported and imported to migrate some of the Assets setup