Query pages by template
Native API 
To get pages by a specified template, perform the following:
    - Get an instance of the 
PageManager object.  
    - Get an instance of the specified template. 
 
    - To get the pages using this template, call the 
Pages extension method of the PageTemplate instance. This extension method is located in the Telerik.Sitefinity.Modules.Pages namespace.  
Use the following code sample:
Fluent API
To get the pages that use a specified template you must get the plural facade for the pages. Then filter the pages by the ID of the specified template and their status. 
To get the query, call the Get method of the facade in the following way: