Dependent drop down not displaying anything

Instead of

PHP Code:

data:"user_dzongkhag="+user_dzongkhag, 


use:

PHP Code:

data: { "user_dzongkhag" : user_dzongkhag }, 


You can also save yourself a lot of time and effort if you put the district names in an array (in your controller). You can pass this array to your view to build the list of districts. And you can pass it to your model to determine which cities belong to the selected district.