execute immediate 'delete from emp where empno = p_my_plsql_variable';

execute immediate 'delete from emp where empno = :b1' using :new.empno;

SQL> create table t ( x int );

Table created.

SQL> create or replace
  2  trigger trg
  3  before insert on t
  4  for each row
  5  declare
  6    v int;
  7  begin
  8    execute immediate 'select count(*) from emp where empno = :b1' using :new.x;
  9  end;
 10  /

Trigger created.