test the signal output of the trigger coil at the CDI connector
test the voltage of the CDI charging coil .. at the CDI
Test the voltage delivered to the spark coil at the coil connector
Check all the wires for damage and bad wire to connector problems.
You might try a known good spark plug from a running GY6 engine.
Here ya go ...
https://www.buggydepot.com/tech-cent...uide-no-spark/