The dropdown needs to have a context to be able to bind the data. Here is a dataview with Feedback as the context of the page. Feedback type is an enumeration attribute of the Feedback object.
Take a look at this for some basics on pages and databinding https://gettingstarted.mendixcloud.com/link/module/5/lecture/243
I have to show the data in dropdown, how can i do that?
I would recommend the DropdownSelector
As far as you Domain model, be sure to have a one to many relationship setup between your DataView object (Container where you place the widget) and the list of objects you wish to show in the dropdown. That should work for you.
Your dropdown is not within a datagrid or listview. You need to have the dropdown within the context of an object. This is the only way that it will be able to get the attribute's data that you are looking for. Add a dataview where the data source is the object where your attribute is and then you will be able to use the drop-down.
I would suggest you go through the learning paths here.