You don't. Sorry to disappoint, but Sonos is not designed or built to support DJing. Live mixing with Sonos, using a line in, will be difficult because of the delay inherent in the system because it has to cater for wireless multiroom audio. If you are just looking for an app that could control Sonos with DJ features, then that would also have technical limitations. Since  music is playing on the Sonos device, not on the phone/tablet/PC that you are using to control it, things like pitch control, cueing tracks, variable crossfade and what have you, would need to be supported by the Sonos firmware, which isn't the case.