Unfortunately there is no way to add markers for songs in uTool for playback yet.
Markers can be created on the fly when a recording is being done on the uTrack-24. Press the PLAY button while a recording is going on to create a new marker. Every button press creates a new marker in the recording.
uTrack24 provides playback from any position too. When playback starts, you can use the rotarty to choose a position and click the rotary to start playback from that position.