You can run the kubectl command with high verbosity level and it should show the curl command and the request body which is internally being used.

kubectl create job --from=cronjob/test-job --v=10



I0324 10:46:36.071067   44400 round_trippers.go:423] curl -k -v -XGET  -H "Accept: application/json" -H "User-Agent: kubectl/v1.17.0 (darwin/amd64) kubernetes/70132b0" 'https://127.0.0.1:32768/apis/batch/v1beta1/namespaces/default/cronjobs/test-job'
I0324 10:46:36.110550   44400 round_trippers.go:443] GET https://127.0.0.1:32768/apis/batch/v1beta1/namespaces/default/cronjobs/test-job 200 OK in 39 milliseconds
I0324 10:46:36.110573   44400 round_trippers.go:449] Response Headers:
I0324 10:46:36.110579   44400 round_trippers.go:452]     Content-Type: application/json
I0324 10:46:36.110585   44400 round_trippers.go:452]     Content-Length: 898
I0324 10:46:36.110590   44400 round_trippers.go:452]     Date: Tue, 24 Mar 2020 05:16:36 GMT
I0324 10:46:36.110631   44400 request.go:1017] Response Body: {"kind":"CronJob","apiVersion":"batch/v1beta1","metadata":{"name":"test-job","namespace":"default","selfLink":"/apis/batch/v1beta1/namespaces/default/cronjobs/test-job","uid":"11813788-123d-4379-a103-79e18c7e954c","resourceVersion":"64182","creationTimestamp":"2020-03-24T05:16:03Z"},"spec":{"schedule":"*/1 * * * *","concurrencyPolicy":"Allow","suspend":false,"jobTemplate":{"metadata":{"name":"test-job","creationTimestamp":null},"spec":{"template":{"metadata":{"creationTimestamp":null},"spec":{"containers":[{"name":"test-job","image":"busybox","resources":{},"terminationMessagePath":"/dev/termination-log","terminationMessagePolicy":"File","imagePullPolicy":"Always"}],"restartPolicy":"OnFailure","terminationGracePeriodSeconds":30,"dnsPolicy":"ClusterFirst","securityContext":{},"schedulerName":"default-scheduler"}}}},"successfulJobsHistoryLimit":3,"failedJobsHistoryLimit":1},"status":{}}
I0324 10:46:36.117139   44400 request.go:1017] Request Body: {"kind":"Job","apiVersion":"batch/v1","metadata":{"name":"job","creationTimestamp":null,"annotations":{"cronjob.kubernetes.io/instantiate":"manual"},"ownerReferences":[{"apiVersion":"apps/v1","kind":"CronJob","name":"test-job","uid":"11813788-123d-4379-a103-79e18c7e954c","controller":true,"blockOwnerDeletion":true}]},"spec":{"template":{"metadata":{"creationTimestamp":null},"spec":{"containers":[{"name":"test-job","image":"busybox","resources":{},"terminationMessagePath":"/dev/termination-log","terminationMessagePolicy":"File","imagePullPolicy":"Always"}],"restartPolicy":"OnFailure","terminationGracePeriodSeconds":30,"dnsPolicy":"ClusterFirst","securityContext":{},"schedulerName":"default-scheduler"}}},"status":{}}
I0324 10:46:36.117189   44400 round_trippers.go:423] curl -k -v -XPOST  -H "Accept: application/json, */*" -H "Content-Type: application/json" -H "User-Agent: kubectl/v1.17.0 (darwin/amd64) kubernetes/70132b0" 'https://127.0.0.1:32768/apis/batch/v1/namespaces/default/jobs'