In Stacked bar chart, sorting is similar to normal sorting from pills.
1. Create a stacked bar chart.
2. Here you can sort using 3 fields 2 from the axis and the the 3rd field from the stacked bar chart.
3. select the field you want to sort normally and apply sort.
4. Right click on the field. Click on sort.
5. Sort dialog box opens.
6. Select the sort options and apply sort.
Hope this helps you.
For an in-depth explanation check out Tableau Training Course details.