I am trying to migrate from . Net 4.7.2 to . Net 8. The thing is that am using webform with dev Express, customcontrol .ascx and .aspx extension can these extensions works with .net 8
No, .NET 8 does not support ASPX and ASCX files. ASPX and ASCX are part of the ASP.NET Web Forms technology, which is considered legacy and is not actively developed or supported in newer versions.
My advice is to turn your ASP.NET Web Forms project into an API project and to start using new .NET technologies for frontend construction.