The reason why this only works on SQL Server is that this is SQL Server language - not standard SQL.
From the code you posted, I infer that you want a simple SELECT query with a parameter - correct?
If so, you should try something like
SELECT "SortNo"
FROM SORTINGRESULT
WHERE U_SORTNO = ?;
HANA studio will ask you for the value of the placeholder (?) upon query execution.
If you actually wanted to create a stored procedure, then this is easily possible too.
Just read the documentation on how to write SQL Script code and you're good.