Given that the data don't include cycles, this is an elementary exercise of traversing a tree (or trees). It is a pity that we cannot pass (hash) object references to user-written functions. If it were possible, then I would have written the recursive part as a user-written function. Here, I use the link blocks instead. The link blocks allow recursive "calls" up to 10 or 11 deep by default. But this limit can be relaxed by using the stack= option to the data statement. (This option is now documented in 9.2.) You need to create and manage call stacks by yourself, though.
   /* test data */
   data one;
      input boss $ sub $;
   cards;
   Jim Kate
   Lisa Jim
   Dave Lisa 
   Dave Erik
   Anna Mary
   Anna Ben
   Erik Anna
   . Dave
   Mary Tom   <-- new data
   Mary Bill  <-- new data
   ;
   run;
 
 
   /* find all the subs */
   %let maxDepth = 100;
   data _null_ / stack=&maxDepth;
 
      /* main */
      link setup;
      do until (end);
         set one end=end;
         thisBoss = boss;
         link find;
      end;
      link out;
      return;
 
      /* helpers */
      setup:
         /* hashes */
         dcl hash in(dataset:"work.one", multidata:'y');
         in.definekey('boss');
         in.definedata('boss','sub'); 
         in.definedone();
         dcl hash out(ordered:'yes');
         out.definekey('boss','sub');
         out.definedata('boss','sub');
         out.definedone();
 
         /* const and global vars */
         retain OK 0;
         length thisBoss $8;
 
         /* call stack */
         array stack_boss[&maxDepth] $8 _temporary_;
         array stack_sub[&maxDepth] $8 _temporary_;
         array stack_rc[&maxDepth] _temporary_;
         array stack_i[&maxDepth] _temporary_;
         array stack_j[&maxDepth] _temporary_;
         stack_top = 0;
      return;
 
      add:
         out.add(key:thisboss, key:sub, data:thisboss, data:sub);
      return;
 
      find:
         link push;
         if missing(thisboss) | missing(sub) then goto outoffind; /* no point adding */
         if out.check(key:thisBoss, key:sub)=OK then goto outoffind; /* already there*/
         link add;
         /* follow */
         boss = sub;
         sub = '';
         /* find_next() gets reset as soon as another find() is called. 
            thus we have to call find() and the number of find_next() 
               for each sibling here. 😞 */
         do i = 0 by 1 until(rc^=OK);
            rc = in.find();
            do j = 1 to i;
               rc = in.find_next();
            end;
            if rc = OK then link find;
         end;
         outoffind: 
         link pop;
      return;
 
      pop:
         boss = stack_boss[top];
         sub = stack_sub[top];
         rc = stack_rc[top];
         i = stack_i[top];
         j = stack_j[top];
         top + (-1);
      return;
 
      push:
         top + 1;
         if top > &maxDepth then do; 
            put "ERROR: stack overflow"; 
            stop; 
         end;
         stack_boss[top] = boss;
         stack_sub[top] = sub;
         stack_rc[top] = rc; 
         stack_i[top] = i;
         stack_j[top] = j;
      return;
 
      out:
         rc = out.output(dataset:"work.two");
      return;
   run;
 
   /* check */
   proc print data=two;
   run;
   /* on lst
   Obs    boss    sub
     1    Anna    Ben
     2    Anna    Bill
     3    Anna    Mary
     4    Anna    Tom
     5    Dave    Anna
     6    Dave    Ben
     7    Dave    Bill
     8    Dave    Erik
     9    Dave    Jim
    10    Dave    Kate
    11    Dave    Lisa
    12    Dave    Mary
    13    Dave    Tom
    14    Erik    Anna
    15    Erik    Ben
    16    Erik    Bill
    17    Erik    Mary
    18    Erik    Tom
    19    Jim     Kate
    20    Lisa    Jim
    21    Lisa    Kate
    22    Mary    Bill
    23    Mary    Tom
   */
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