Launch PlotJuggler and enable the UDP server:
Subscribe like you normally would and pipe the JSON output to the UDP port of PlotJuggler (add +M if you also want the metadata like the timestamps, source node-ID, etc):
y sub 1250 1251 --sync | nc -u localhost 9870
Drag & drop the values you need onto the plotting area:
Here’s a relevant thread I just started covering some Cyphal-specific usability issues/questions: Plotting real-time JSON stream from another application · Discussion #639 · facontidavide/PlotJuggler · GitHub