You can create a user control (.ascx file) and query in the code behind the employees who have birthday in the next three weeks. You can find samples on how to retrieve employees through filtering and how to work with your dynamic module programatically in the code reference which is automatically generated for your custom module created using the Module Builder. To view the generated code samples please go to Administration -> Module builder
and select your module.
Then please click on the Code reference for < module name>
link which is on the right-hand side of the page. Here is a screenshot
for your convenience.
After you get the employees filtered by their birth date in the code behind, you can bind them to a ListView or any other control in order to display the desired information about the employees on the frontend.
After performing the above, you can register the user control using Sitefinity Thunder as described in the following documentation article
and add the widget on your page
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Sitefinity CMS Ideas&Feedback Portal
and vote to affect the priority of the items