There are ACL's on table sn_customerservice_m2m_asset_contact that prevents creation of contact records to associate with assets.
Steps to see the behavior is:
1. Navigate Knowledge>asset, open the asset record.
2. Under the related record 'asset contact', a user who does not have admin role will not be able to view or create 'asset contact'.
- Navigate to Roles and create a new role for example 'A'.
- Associate users with this role.
- Navigate to System Security>Access Control (ACL) and search for name 'sn_customerservice_m2m_asset_contact'.
- On the read, write and create ACL's that are returned in step 3, modify the requires role section to include role A created in step 1.