Solution:
[jsoncontentimporter url=https://cast02.siamsa.ie/public/radio_siamsa/api/live/nowplaying/radio_siamsa basenode=now_playing.song]
{text}<img src={art}>
[/jsoncontentimporter]
or:
[jsoncontentimporter url=https://cast02.siamsa.ie/public/radio_siamsa/api/live/nowplaying/radio_siamsa]
{subloop:now_playing:-1}
{subloop:now_playing.song:-1}
{now_playing.song.text}<img src={now_playing.song.art}>
{/subloop:now_playing.song}
{/subloop:now_playing}
[/jsoncontentimporter]