Jaka jest różnica między szkoda mi i szkoda mojego wysiłku ?Możesz podać przykładowe zdania.

Szkoda mi:
It's more general and requires some auxiliary words. It might mean that shomething is not worth something of yours. It also means that woy feel sorry for something/someone. Examples:
Szkoda mi pieniędzy na to wesele. - I don't want to spend/waste money on that wedding.
Szkoda mi czasu na chodzenie po sklepach. - I don't want to spend/waste time on shopping.
Szkoda mi tego psa, chyba jest mu zimno. - I feel sorry for that dog, I think he's cold.
Szkoda mi Ciebie. - I feel sorry for you (could be positive or negative, depending on context).

Szkoda mojego wysiłku.
It's more specific and means just: It is/was/will be not worth my effort. It might have nuance of feeling bad about somebody neglecting your good intention/effort.
Szkoda mojego wysiłku jeśli i tak tego nie zamierzasz tego nosić. It's not worth my effort if you are not going to wear it.
Tego nikt nie przeczyta, szkoda mojego wysiłku. - It's not worht my effort, nobody will read this anyway.