A job whose execution has ended due to cancellation or an unhandled exception is considered cancelled. When a job has been cancelled, the information about the cancellation can be obtained through the getCancellationException() function. This function will return a CancellationException, which can be used to retrieve information such as the cause of the cancellation, if it was set. Here's an example:

fun main(args: Array<String>) = runBlocking {
    val job = launch {
        delay(5000)
    }

    delay(2000)

    // cancel
    job.cancel(cause = Exception("Tired of waiting"))

    val cancellation = job.getCancellationException()
    cancellation.cause // Exception("Tired of waiting")
}

In order to differentiate between a job that was cancelled and one that failed due to exception, you are encouraged to set a CoroutineExceptionHandler to it and process the cancellation there, as shown:

fun main(args: Array<String>) = runBlocking {
    val exceptionHandler = CoroutineExceptionHandler {
        _: CoroutineContext, throwable: Throwable ->
        println("Job cancelled due to ${throwable.message}")
    }

    launch(exceptionHandler) {
        TODO("Not implemented yet!")
    }

    delay(2000)
}

You can also use invokeOnCompletion(), as follows:

fun main(args: Array<String>) = runBlocking<Unit> {
    launch {
        TODO("Not implemented yet!")
    }.invokeOnCompletion { cause ->
        cause?.let {
            println("Job cancelled due to ${it.message}")
        }
    }

    delay(2000)
}