There is not any trigger creation "in" ASP.Net.
But you can create a trigger "through" your ASP.Net in the SQL-Server.
Many ways. For example:
You must know the T-SQl syntax and command of creating trigger: Look at the link
You must know about
in C#. Loot at the link
I really think it would be a pity if you don't use dynamic SQL Commands. You can create trigger in the SQL-Server through itself, when you are developing the application (not runtime).
Creating a trigger dynamically(!) will complicate your program and using dynamic commands maybe a security risk (Look at this