Snippets are reusable page components within Mendix.
You must set the entity that you use within snippet at the top, refer image below
Once you set the entity, then there is no need to have data view within snippet. You can use the attributes directly with appropriate widgets.
Remove your data view with in snippet and put the attributes within dataview directly.
When you call a snippet from a different page, then you call it from within dataview, datagrid, template grid or list view for that entity.
Hope this helps. Happy learning