I'm not using NetBeans, but I can see command line arguments in IntelliJ. They are printed as first log line in the Run window. Maybe you have something similar.
See the line Executing task 'clean -i --console=plain'

Didn't find a way of how to debug command line argument options within Gradle.
For all other project and system properties and arguments to Gradle JVM itself you can use following script:
import java.lang.management.RuntimeMXBean
import java.lang.management.ManagementFactory
println("==== START EXT Gradle Properties ====")
project.properties.ext.properties.forEach{key, value ->
println("KEY: $key, VALUE is: $value")
}
println("==== START Gradle Properties ====")
project.properties.forEach{key, value ->
println("KEY: $key, VALUE is: $value")
}
println("==== START Gradle JVM Arguments ====")
RuntimeMXBean runtimeMXBean = ManagementFactory.getRuntimeMXBean();
List<String> jvmArgs = runtimeMXBean.getInputArguments();
for (String arg : jvmArgs) {
System.out.println(arg);
}
println("==== START System Properties ====")
System.getenv()
System.getProperties().forEach{key, value ->
println("KEY: $key, VALUE is: $value")
}