If you look under the table menu, there are a bunch of commands for reorganizing data tables. One of these is sort. You can add the column(s) of interest and specify ascending or descending. JMP can then either replace your table or create a new one.
If you only want to sort one column, you can right mouse click on the header of the column and the second to the last option is sort. To sort it the descending, sort it again with the right mouse click.