The uTrack24 does not change the sample rate of the song.
So if your system running at 48kHz, you need to have the audio files on the same sample rate. You can do that easily by set 48kHz in the uTool during the song creation or you can also edit your songs.
But if you are using analog outputs on the uTrack24 the two device not necessarily has to be synced together with wordclock.
However if you want it you can do it. Set up the mixer as a clock master, then use the wordclock (in) connector on the uTrack24 and set the clock to wordclock.
Here you can find details about the clocking