To collect Onload logs, get a root shell in the nodes and run each required onload_mibdump or onload_stackdump command there:
$ oc debug node/compute-0
sh-4.4# chroot /host/
sh-4.4# /opt/onload/usr/bin/onload_stackdump
#stack-id stack-name pids
0 - 651852
The Onload files are in the /opt/onload/ directory in the hosts with the deployed Onload.