Hi Praven ,
As Johan mentioned before maybe the attribute is not included in visittype . Can you also share domain model of the entity or some more explanation ?
I realized later that you are trying to reach an attribute within the visittype entity. But there is a Location entity on the page as the current object. That's why you only see the association in the dropdown (to choose) . If you bring the page the object (visittype) you want to see the attributes of it in dropdown, you can access the attributes .
You can add the enumeration attribute on your page. this will be added as radiobutton but you can change it in the menu.
Did you add the enumeration to an attribute on the entity visaType?
Also see Drop-Down | Mendix Documentation for some documentation on dropdowns.
Hope this helps!