Hi division odt,
Depends. 🙂
Do you want to block access to all attribute data altogether, i.e. not only the attribute table but also the popup, or are you really only talking about the tabular view of the data, i.e. the attribute table only?
In the first case you might create a view of your data with all the attribute data removed.
In the second case you can - as Mark Donnelly indicates - configure the app to not show the attribute table.
Using the Web AppBuilder for ArcGIS, on the Widget tab, you can turn off the visibility of the Attribute Table (see screen capture attached). In this case users will be able to access the attribute data by clicking an object to open the popup, but the will not be able to open the attribute table itself.
Please let us know whether you have found a solution to your issue.
BR,
Egge-Jan