First, in Oracle SELECT needs a FROM clause. The system table DUAL is provided for this, although in principle it's no different from any other table.

However, PL/SQL has an assignment operator ":=", so you could code for example,

DECLARE
v_emp1 emp.emp1%TYPE := :new.emp1;
BEGIN
...code using v_emp1...
END;

But why go to the trouble of duplicating the variable at all? I would just use :new.emp1 directly in the code.