Do you mean to find out the sort order of an existing table?
To do that go to the SAS dictionary tables (sashelp.vcolumn) and look at the field sortedby for the table that you want.
Do you mean to create a SAS table and then tell it what the sort order should be?
PROC DATASETS among other things lets you change the metadata of a dataset. Specifically for your case, you can tell SAS what the sort order is with out sorting the file.
However, this may be quite dangerous for if you insert records not in the sort order sequence that you specify. Merges and other by group processing will not work. I would just sort the file after I updated it or index it.
But below is the example anyways.
create table One
proc datasets library=work nolist;
modify One (sortedby=x1 x2);