Here you go

1..how to call server script in client script ? GlideAjax. You need to use GlideAjax for this

2..how to call client script in server script? there is no out of box way, but you can achieve this based on the use case

3..how to call script include in business rules or client script ? You call the script includes directly in business rule by using new operator

4..how to call   UI script in client script or server script or business rules ? UI script can be called for ma client script directly by calling the function.