Groove Machine Mobile / FL Studio Groove uses the default audio device.
In FL Studio Groove on Win8, it is possible to change this setting in the Windows mixer, if you have more than one sound card and want to send sound somewhere specific.
FL Studio Groove is not using ASIO, as Windows (since Windows Vista) has a more effective technology avialable - XAudio. It gives the same or even better latency than ASIO, and is used for XBox games.