When creating Task Template from Alert Action Rule, all reference field are showing as text field
This is expected behavior when open another popup window from a popup window.
However, for fields that are defined as reference, limited lookup functionality do exists in popup windows.
When user starts typing in such field, a drop down list is displayed allowing the user to select relevant item - see attached screenshot below.
Create create a Task Template via:
Event Management > Settings > Task templates > New
Then the Service field is showing as reference correctly.
Once task template is created, select it in the Alert Action Rule.