In Tasks, click on any list that is not a smartlist (as far as I know you cant publish smartlists, but you can make Rss feeds to them if you need that).

Then, to the right, you will see information about the list (name, number of tasks, etc). Just above that is the Publish tab (beside "list" and "share")

See it now? Also, as far as I know, you can se which lists are published in "settings", then "info". Lists are not published by default.

Victor