When working on an Android module, Studio 3.1.2 doesn't shows the targets of the ant build.
Just create an Android module via Studio and select build.xml. Then right-click "Run As" to bring up "External Tools Configurations" window.
If i switch to the mainstream TiStudio, then it works. Build targets of Ant working under Titanium Studio, build: 22.214.171.124302191606