Think about what you do to get dbms_output output in SQLPlus in a local database
1) you *enable* it (set serverout on)
2) then make calls to dbms_output
So you need to do the *same* for the db link session
SQL> declare
2 x varchar2(1000);
3 status int;
4 begin
5 dbms_output.enable@db1; <<<< ======
6 p@np12;
7 loop
8 dbms_output.get_line@db1( x,status);
9 exit when status != 0;
10 dbms_output.put_line(x)
11 end loop;
12 end;
13 /